Quantum error correction protects fragile quantum information by encoding it into a larger quantum system1,2. These extra degrees of freedom enable the detection and correction of errors, but also increase the control complexity of the encoded logical qubit. Fault-tolerant circuits contain the spread of errors while controlling the logical qubit, and are essential for realizing error suppression in practice3,4,5,6. Although fault-tolerant design works in principle, it has not previously been demonstrated in an error-corrected physical system with native noise characteristics. Here we experimentally demonstrate fault-tolerant circuits for the\ preparation, measurement, rotation and stabilizer measurement of a Bacon{\textendash}Shor logical qubit using 13 trapped ion qubits. When we compare these fault-tolerant protocols to non-fault-tolerant protocols, we see significant reductions in the error rates of the logical primitives in the presence of noise. The result of fault-tolerant design is an average state preparation and measurement error of 0.6\ per cent and a Clifford gate error of 0.3\ per cent after offline error correction. In addition, we prepare magic states with fidelities that exceed the distillation threshold7, demonstrating all of the key single-qubit ingredients required for universal fault-tolerant control. These results demonstrate that fault-tolerant circuits enable highly accurate logical primitives in current quantum systems. With improved two-qubit gates and the use of intermediate measurements, a stabilized logical qubit can be achieved.

}, keywords = {error correction, Ion trap, quantum computing}, doi = {10.1038/s41586-021-03928-y}, url = {https://doi.org/10.1038/s41586-021-03928-y}, author = {Laird Egan and Dripto M. Debroy and Crystal Noel and Andrew Risinger and Daiwei Zhu and Debopriyo Biswas and Michael Newman and Muyuan Li and Kenneth R. Brown and Marko Cetina and Christopher Monroe} } @article { WOS:000712467500001, title = {Feedback-stabilized dynamical steady states in the Bose-Hubbard model}, journal = {Phys. Rev. Res.}, volume = {3}, number = {4}, year = {2021}, month = {OCT 27}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The implementation of a combination of continuous weak measurement and classical feedback provides a powerful tool for controlling the evolution of quantum systems. In this paper, we investigate the potential of this approach from three perspectives. First, we consider a double-well system in the classical large-atom-number limit, deriving the exact equations of motion in the presence of feedback. Second, we consider the same system in the limit of small atom number, revealing the effect that quantum fluctuations have on the feedback scheme. Finally, we explore the behavior of modest-sized Hubbard chains using exact numerics, demonstrating the near-deterministic preparation of number states, a tradeoff between local and nonlocal feedback for state preparation, and evidence of a feedback-driven symmetry-breaking phase transition.}, doi = {10.1103/PhysRevResearch.3.043075}, author = {Young, Jeremy T. and Gorshkov, V, Alexey and Spielman, I. B.} } @article { WOS:000704987700003, title = {Fluctuation-dissipation relation for a quantum Brownian oscillator in a parametrically squeezed thermal field}, journal = {Ann. Phys.}, volume = {433}, year = {2021}, month = {OCT}, publisher = {ACADEMIC PRESS INC ELSEVIER SCIENCE}, type = {Article}, abstract = {In this paper we study the nonequilibrium evolution of a quantum Brownian oscillator, modeling the internal degree of freedom of a harmonic atom or an Unruh-DeWitt detector, coupled to a nonequilibrium and nonstationary quantum field bath and inquire whether a fluctuation-dissipation relation (FDR) can exist after/if it approaches equilibration. This is a nontrivial issue because a squeezed field bath cannot reach equilibration and yet, as this work shows, the system oscillator indeed can, which is a necessary condition for FDRs. We discuss three different settings: (A) The bath field essentially remains in a squeezed thermal state throughout, whose squeeze parameter is a mode- and time-independent constant. This situation is often encountered in quantum optics and quantum thermodynamics. (B) The bath field is initially in a thermal state, but is subjected to a parametric process leading to mode- and time-dependent squeezing. This scenario is encountered in cosmology and dynamical Casimir effects. The squeezing in the bath in both types of processes will affect the oscillator{\textquoteright}s nonequilibrium evolution. We show that at late times it approaches equilibration and this stationarity condition warrants the existence of a FDR. The trait of squeezing is marked by the oscillator{\textquoteright}s effective equilibrium temperature, and the proportionality factor in the FDR is only related to the stationary component of the noise kernel of the bath field. Setting (C) is more subtle: A finite system-bath coupling strength can set the oscillator in a squeezed state even though the bath field is stationary and does not engage in any parametric process. The squeezing of the system in this case is in general time-dependent but becomes constant when the internal dynamics is fully relaxed. We begin with comments on the broad range of physical processes involving squeezed thermal baths and end with some remarks on the significance of FDRs in capturing the essence of quantum backreaction in nonequilibrium and stochastic systems. (C) 2021 Elsevier Inc. All rights reserved.}, keywords = {Fluctuation-dissipation relation, nonequilibrium field theory, Parametric oscillator, Squeezed thermal field, Strongly interacting Gaussian system, Time-dependent background}, issn = {0003-4916}, doi = {10.1016/j.aop.2021.168594}, author = {Hsiang, Jen-Tsung and Hu, Bei-Lok} } @article { WOS:000704419000003, title = {Fragile versus stable two-dimensional fermionic quasiparticles}, journal = {Phys. Rev. B}, volume = {104}, number = {12}, year = {2021}, month = {SEP 13}, publisher = {AMER PHYSICAL SOC}, type = {Editorial Material}, abstract = {We provide a comprehensive theoretical investigation of the Fermi liquid quasiparticle description in two-dimensional electron gas interacting via the long-range Coulomb interaction by calculating the electron self-energy within the leading-order approximation, which is exact in the high-density limit. We find that the quasiparticle energy is larger than the imaginary part of the self-energy up to very high energies, implying that the basic Landau quasiparticle picture is robust up to far above the Fermi energy. We find, however, that the quasiparticle picture becomes fragile in a small discrete region around a critical wave vector where the quasiparticle spectral function strongly deviates from the expected quasiparticle Lorentzian line shape with a vanishing renormalization factor. We show that such a non-Fermi liquid behavior arises due to the coupling of quasiparticles with the collective plasmon mode. This situation is somewhat intermediate between the one-dimensional interacting electron gas (i.e., Luttinger liquid), where the Landau Fermi liquid theory completely breaks down since only bosonic collective excitations exist, and three-dimensional electron gas, where quasiparticles are well-defined and more stable against interactions than in one and two dimensions. We use a number of complementary definitions for a quasiparticle to examine the interacting spectral function, contrasting two-dimensional and three-dimensional situations critically.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.104.125118}, author = {Ahn, Seongjin and Das Sarma, Sankar} } @article {mueller_single-particle-like_2021, title = {From single-particle-like to interaction-mediated plasmonic resonances in graphene nanoantennas}, journal = {J. Appl. Phys.}, volume = {129}, number = {9}, year = {2021}, note = {Place: 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA Publisher: AMER INST PHYSICS Type: Article}, month = {mar}, abstract = {Plasmonic nanostructures attract tremendous attention as they confine electromagnetic fields well below the diffraction limit while simultaneously sustaining extreme local field enhancements. To fully exploit these properties, the identification and classification of resonances in such nanostructures is crucial. Recently, a novel figure of merit for resonance classification has been proposed [Muller et al., J. Phys. Chem. C 124, 24331-24343 (2020)] and its applicability was demonstrated mostly to toy model systems. This novel measure, the energy-based plasmonicity index (EPI), characterizes the nature of resonances in molecular nanostructures. The EPI distinguishes between either a single-particle-like or a plasmonic nature of resonances based on the energy space coherence dynamics of the excitation. To advance the further development of this newly established measure, we present here its exemplary application to characterize the resonances of graphene nanoantennas. In particular, we focus on resonances in a doped nanoantenna. The structure is of interest, as a consideration of the electron dynamics in real space might suggest a plasmonic nature of selected resonances in the low doping limit but our analysis reveals the opposite. We find that in the undoped and moderately doped nanoantenna, the EPI classifies all emerging resonances as predominantly single-particle-like, and only after doping the structure heavily, the EPI observes plasmonic response.}, issn = {0021-8979}, doi = {10.1063/5.0038883}, author = {Mueller, Marvin M. and Kosik, Miriam and Pelc, Marta and Bryant, Garnett W. and Ayuela, Andres and Rockstuhl, Carsten and Slowik, Karolina} } @article { WOS:000693643600008, title = {Frustration-induced anomalous transport and strong photon decay in waveguide QED}, journal = {Phys. Rev. Res.}, volume = {3}, number = {3}, year = {2021}, month = {SEP 7}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the propagation of photons in a one-dimensional environment consisting of two noninteracting species of photons frustratingly coupled to a single spin 1/2. The ultrastrong frustrated coupling leads to an extreme mixing of the light and matter degrees of freedom, resulting in the disintegration of the spin and a breakdown of the {\textquoteleft}{\textquoteleft}dressed-spin,{{\textquoteright}{\textquoteright}} or polaron, description. Using a combination of numerical and analytical methods, we show that the elastic response becomes increasingly weak at the effective spin frequency, showing instead an increasingly strong and broadband response at higher energies. We also show that the photons can decay into multiple photons of smaller energies. The total probability of these inelastic processes can be as large as the total elastic scattering rate, or half of the total scattering rate, which is as large as it can be. The frustrated spin induces strong anisotropic photon-photon interactions that are dominated by interspecies interactions. Our results are relevant to state-of-the-art circuit and cavity quantum electrodynamics experiments.}, doi = {10.1103/PhysRevResearch.3.L032058}, author = {Belyansky, Ron and Whitsitt, Seth and Lundgren, Rex and Wang, Yidan and Vrajitoarea, Andrei and Houck, Andrew A. and Gorshkov, V, Alexey} } @article {hurst_feedback_2020, title = {Feedback induced magnetic phases in binary {Bose}-{Einstein} condensates}, journal = {Phys. Rev. Res.}, volume = {2}, number = {4}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {dec}, abstract = {Weak measurement in tandem with real-time feedback control is a new route toward engineering novel nonequilibrium quantum matter. Here we develop a theoretical toolbox for quantum feedback control of multicomponent Bose-Einstein condensates (BECs) using backaction-limited weak measurements in conjunction with spatially resolved feedback. Feedback in the form of a single-particle potential can introduce effective interactions that enter into the stochastic equation governing system dynamics. The effective interactions are tunable and can be made analogous to Feshbach resonances-spin independent and spin dependent-but without changing atomic scattering parameters. Feedback cooling prevents runaway heating due to measurement backaction and we present an analytical model to explain its effectiveness. We showcase our toolbox by studying a two-component BEC using a stochastic mean-field theory, where feedback induces a phase transition between easy-axis ferromagnet and spin-disordered paramagnet phases. We present the steady-state phase diagram as a function of intrinsic and effective spin-dependent interaction strengths. Our result demonstrates that closed-loop quantum control of Bose-Einstein condensates is a powerful tool for quantum engineering in cold-atom systems.}, doi = {10.1103/PhysRevResearch.2.043325}, author = {Hurst, Hilary M. and Guo, Shangjie and Spielman, I. B.} } @article { ISI:000571392500002, title = {Fermion parity gap and exponential ground state degeneracy of the one-dimensional Fermi gas with intrinsic attractive interaction}, journal = {Phys. Rev. B}, volume = {102}, number = {12}, year = {2020}, month = {SEP 21}, pages = {125135}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We examine the properties of a one-dimensional (1D) Fermi gas with attractive intrinsic (Hubbard) interactions in the presence of spin-orbit coupling and Zeeman field by numerically computing the pair binding energy, excitation gap, and susceptibility to local perturbations using the density matrix renormalization group. Such a system can, in principle, be realized in a system of ultracold atoms confined in a 1D optical lattice. We note that, in the presence of spatial interfaces introduced by a smooth parabolic potential, the pair binding and excitation energy of the system decays exponentially with the system size, pointing to the existence of an exponential ground state degeneracy, and is consistent with recent works. However, the susceptibility of the ground state degeneracy of this number-conserving system to local impurities indicates that the energy gap vanishes as a power law with the system size in the presence of local perturbations. We compare this system with the more familiar system of an Ising antiferromagnet in the presence of a transverse field realized with Rydberg atoms and argue that the exponential splitting in the clean number-conserving 1D Fermi system is similar to a phase with only conventional order.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.125135}, author = {Roy, Monalisa Singh and Kumar, Manoranjan and Sau, Jay D. and Tewari, Sumanta} } @article { ISI:000579337200002, title = {Fermi-surface topology and renormalization of bare ellipticity in an interacting anisotropic electron gas}, journal = {Phys. Rev. B}, volume = {102}, number = {16}, year = {2020}, month = {OCT 19}, pages = {161114}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We investigate effects of electron-electron interactions on the shape of the Fermi surface in an anisotropic two-dimensional electron gas using the {\textquoteleft}{\textquoteleft}RPA-GW{{\textquoteright}{\textquoteright}} self-energy approximation. We find that the interacting Fermi surface deviates from an ellipse but not in an arbitrary way. The interacting Fermi surface has only two qualitatively distinct shapes for most values of r(s). The Fermi surface undergoes two distinct transitions between these two shapes as r(s) increases. For larger r(s), the degree of the deviation from an ellipse rapidly increases, but, in general, our theory provides a justification for the widely used elliptical Fermi-surface approximation, even for the interacting system, since the nonelliptic corrections are quantitatively rather small except for very large r(s).}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.161114}, author = {Ahn, Seongjin and Das Sarma, S.} } @article {alavirad_ferromagnetism_2020, title = {Ferromagnetism and its stability from the one-magnon spectrum in twisted bilayer graphene}, journal = {Phys. Rev. B}, volume = {102}, number = {23}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {dec}, abstract = {We study ferromagnetism and its stability in twisted bilayer graphene. We work with a Hubbard-like interaction that corresponds to the screened Coulomb interaction in a well-defined limit where the Thomas-Fermi screening length l(TF) is much larger than monolayer graphene{\textquoteright}s lattice spacing l(g) {\textless}{\textless} l(TF) and much smaller than the moire superlattice{\textquoteright}s spacing l(TF) {\textless}{\textless} l(moire). We show that in the perfectly flat band {\textquotedblleft}chiral{\textquotedblright} limit and at filling fractions +/- 3/4, the saturated ferromagnetic (spin- and valley-polarized) states are ideal ground-state candidates in the large band-gap limit. By assuming a large enough substrate (hBN) induced sublattice potential, the same argument can be applied to filling fractions +/- 1/4. We estimate the regime of stability of the ferromagnetic phase around the chiral limit by studying the exactly calculated spectrum of one-magnon excitations. The instability of the ferromagnetic state is signaled by a negative magnon excitation energy. This approach allows us to deform the results of the idealized chiral model (by increasing the bandwidth and/or modified interactions) toward more realistic systems. Furthermore, we use the low-energy part of the exact one-magnon spectrum to calculate the spin-stiffness of the Goldstone modes throughout the ferromagnetic phase. The calculated value of spin-stiffness can determine the excitation energy of charged skyrmions.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.235123}, author = {Alavirad, Yahya and Sau, Jay} } @article { ISI:000529804100001, title = {Ferromagnetism and superconductivity in twisted double bilayer graphene}, journal = {Phys. Rev. B}, volume = {101}, number = {15}, year = {2020}, month = {APR 30}, pages = {155149}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We present a theory of competing ferromagnetic and superconducting orders in twisted double bilayer graphene. In our theory, ferromagnetism is induced by Coulomb repulsion, while superconductivity with intervalley equal-spin pairing can be mediated by electron-acoustic phonon interactions. We calculate the transition temperatures for ferromagnetism and superconductivity as a function of moire band filling factor, and find that superconducting domes can appear on both the electron and hole sides of the ferromagnetic insulator at half filling. We show that the ferromagnetic insulating gap has a dome shape dependence on the layer potential difference, which provides an explanation to the experimental observation that the ferromagnetic insulator only develops over a finite range of external displacement field. We also verify the stability of the half filled ferromagnetic insulator against two types of collective excitations, i.e., spin magnons and valley magnons.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.101.155149}, author = {Wu, Fengcheng and Das Sarma, Sankar} } @article { ISI:000559739800002, title = {Feshbach Resonances in p-Wave Three-Body Recombination within Fermi-Fermi Mixtures of Open-Shell Li-6 and Closed-Shell Yb-173 Atoms}, journal = {Phys. Rev. X}, volume = {10}, number = {3}, year = {2020}, month = {AUG 14}, pages = {031037}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We report on the observation of magnetic Feshbach resonances in a Fermi-Fermi mixture of ultracold atoms with extreme mass imbalance and on their unique p-wave dominated three-body recombination processes. Our systemconsists of open-shell alkali-metal Li-6 and closed-shell Yb-173 atoms, both spin polarized and held at various temperatures between 1 and 20 mu K. We confirmthat Feshbach resonances in this systemare solely the result of a weak separation-dependent hyperfine coupling between the electronic spin of Li-6 and the nuclear spin of Yb-173. Our analysis also shows that three-body recombination rates are controlled by the identical fermion nature of the mixture, even in the presence of s-wave collisions between the two species and with recombination rate coefficients outside the Wigner threshold regime at our lowest temperature. Specifically, a comparison of experimental and theoretical line shapes of the recombination process indicates that the characteristic asymmetric line shape as a function of applied magnetic field and a maximum recombination rate coefficient that is independent of temperature can only be explained by triatomic collisions with nonzero, p-wave total orbital angular momentum. The resonances can be used to form ultracold doublet ground-state molecules and to simulate quantum superfluidity in mass-imbalanced mixtures.}, issn = {2160-3308}, doi = {10.1103/PhysRevX.10.031037}, author = {Green, Alaina and Li, Hui and Toh, Jun Hui See and Tang, Xinxin and McCormick, Katherine C. and Li, Ming and Tiesinga, Eite and Kotochigova, Svetlana and Gupta, Subhadeep} } @article { ISI:000552576600008, title = {Fidelity of a sequence of SWAP operations on a spin chain}, journal = {Phys. Rev. B}, volume = {102}, number = {3}, year = {2020}, month = {JUL 27}, pages = {035439}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We consider the {\textquoteleft}{\textquoteleft}transport{{\textquoteright}{\textquoteright}} of the state of a spin across a Heisenberg-coupled spin chain via the use of repeated SWAP gates, starting with one of two states-one in which the leftmost spin is down and the others up, and one in which the leftmost two spins are in a singlet state (i.e., they are entangled), and the others are again all up. More specifically, we transport the state of the leftmost spin in the first case and the next-to-leftmost spin in the second to the other end of the chain, and then back again. We accomplish our SWAP operations here by increasing the exchange coupling between the two spins that we operate on from a base value J to a larger value J(SWAP) for a time t = pi(h) over bar /4J(SWAP). We determine the fidelity of this sequence of operations in a number of situations-one in which only nearest-neighbor coupling exists between spins and there is no magnetic dipole-dipole coupling or noise (the most ideal case), one in which we introduce next-nearest-neighbor coupling, but none of the other effects, and one in which all of these effects are present. In the last case, the noise is assumed to be quasistatic, i.e., the exchange couplings are each drawn from a Gaussian distribution, truncated to only nonnegative values. We plot the fidelity as a function of JSWAP to illustrate various effects, namely crosstalk due to coupling to other spins, as well as noise, that are detrimental to our ability to perform a SWAP operation. Our theory should be useful to the ongoing experimental efforts in building semiconductor-based spin quantum computer architectures.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.035439}, author = {Throckmorton, Robert E. and Das Sarma, S.} } @article { ISI:000536153200001, title = {Figures of merit for quantum transducers}, journal = {Quantum Sci. Technol.}, volume = {5}, number = {3}, year = {2020}, month = {JUL}, pages = {034009}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {Recent technical advances have sparked renewed interest in physical systems that couple simultaneously to different parts of the electromagnetic spectrum, thus enabling transduction of signals between vastly different frequencies at the level of single quanta. Such hybrid systems have demonstrated frequency conversion of classical signals and have the potential of enabling quantum state transfer, e.g., between superconducting circuits and traveling optical signals. This article describes a simple approach for the theoretical characterization of the performance of quantum transducers. Given that, in practice, one cannot attain ideal one-to-one quantum conversion, we explore how imperfections impact the performance of the transducer in various scenarios. We quantify how knowledge of the well-established transducer parameters signal transfer efficiency eta and added noise N suffices to assess its performance in a variety of transduction schemes ranging from classical signal detection to applications for quantum information processing.}, keywords = {quantum sensing, quantum transduction, transduction}, issn = {2058-9565}, doi = {10.1088/2058-9565/ab8962}, author = {Zeuthen, Emil and Schliesser, Albert and Sorensen, Anders S. and Taylor, Jacob M.} } @article { ISI:000535764500002, title = {Filter-free single-photon quantum dot resonance fluorescence in an integrated cavity-waveguide device}, journal = {Optica}, volume = {7}, number = {5}, year = {2020}, month = {MAY 20}, pages = {380-385}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {Semiconductor quantum dots embedded in micropillar cavities are excellent emitters of single photons when pumped resonantly. Often, the same spatial mode is used to both resonantly excite a quantum-dot state and to collect the emitted single photons, requiring cross polarization to reduce the uncoupled scattered laser light. This inherently reduces the source brightness to 50\%. Critically, for some quantum applications the total efficiency from generation to detection must be over 50\%. Here, we demonstrate a resonant-excitation approach to creating single photons that is free of any cross polarization, and in fact any filtering whatsoever. It potentially increases single-photon rates and collection efficiencies, and simplifies operation. This integrated device allows us to resonantly excite single quantum-dot states in several cavities in the plane of the device using connected waveguides, while the cavity-enhanced single-photon fluorescence is directed vertically (off-chip) in a Gaussian mode. We expect this design to be a prototype for larger chip-scale quantum photonics. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {2334-2536}, doi = {10.1364/OPTICA.382273}, author = {Huber, Tobias and Davanco, Marcelo and Muller, Markus and Shuai, Yichen and Gazzano, Olivier and Solomon, Glenn S.} } @article { ISI:000562933100003, title = {Finite-temperature spectroscopy of dirty helical Luttinger liquids}, journal = {Phys. Rev. B}, volume = {102}, number = {8}, year = {2020}, month = {AUG 27}, pages = {085152}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We develop a theory of finite-temperature momentum-resolved tunneling spectroscopy (MRTS) for disordered, interacting, two-dimensional, topological-insulator edges. The MRTS complements conventional electrical transport measurement in characterizing the properties of the helical Luttinger liquid edges. Using the standard bosonization technique, we study low-energy spectral function and the MRTS tunneling current, providing a detailed description controlled by disorder, interaction, and temperature, taking into account Rashba spin-orbit coupling, interedge interaction, and distinct edge velocities. Our theory provides a systematic description of the spectroscopic signals in the MRTS measurement we hope will stimulate future experimental studies on the two-dimensional time-reversal invariant topological insulator.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.102.085152}, author = {Hsieh, Tzu-Chi and Chou, Yang-Zhi and Radzihovsky, Leo} } @article {hsiang_fluctuation-dissipation_2020, title = {Fluctuation-dissipation relation for open quantum systems in a nonequilibrium steady state}, journal = {Phys. Rev. D}, volume = {102}, number = {10}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {nov}, abstract = {Continuing our work on the nature and existence of fluctuation-dissipation relations (FDR) in linear and nonlinear open quantum systems [J.-T. Hsiang, B. L. Hu, and S.-Y. Lin, Phys. Rev. D 100, 025019 (2019); J.-T. Hsiang, B. L. Hu, S.-Y. Lin, and K. Yamamoto, Phys. Lett. B 795, 694 (2019); J.-T. Hsiang and B. L. Hu, Physics (Utrecht) 1, 430 (2019); J.-T. Hsiang and B. L. Hu, Phys. Rev. D 101, 125003 (2020)], here we consider such relations when a linear system is in a nonequilibrium steady state (NESS). With the model of two-oscillators (considered as a short harmonic chain with the two ends) each connected to a thermal bath of different temperatures we find that when the chain is fully relaxed due to interaction with the baths, the relation that connects the noise kernel and the imaginary part of the dissipation kernel of the chain in one bath does not assume the conventional form for the FDR in equilibrium cases. There exists an additional term we call the {\textquotedblleft}bias current{\textquotedblright} that depends on the difference of the bath{\textquoteright}s initial temperatures and the interoscillator coupling strength. We further show that this term is related to the steady heat flow between the two baths when the system is in an NESS. The ability to know the real-time development of the interheat exchange (between the baths and the end-oscillators) and the intraheat transfer (within the chain) and their dependence on the parameters in the system offers possibilities for quantifiable control, and in the design of quantum heat engines, or thermal devices.}, issn = {2470-0010}, doi = {10.1103/PhysRevD.102.105006}, author = {Hsiang, Jen-Tsung and Hu, Bei-Lok} } @article {hsiang_fluctuation-dissipation_2020-1, title = {Fluctuation-dissipation relation from the nonequilibrium dynamics of a nonlinear open quantum system}, journal = {Phys. Rev. D}, volume = {101}, number = {12}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, month = {jun}, abstract = {Continuing our inquiry into the conditions when fluctuation-dissipation relations (FDR) may appear in the context of nonequilibrium dynamics of open quantum systems (over and beyond the conventional FDR from linear response theory) we turn to non-Gaussian systems and consider this issue for an anharmonic quantum oscillator interacting with a scalar quantum field bath. We present the general nonperturbative expressions for the rate of energy (power) exchange between the anharmonic oscillator and its thermal bath. For the cases that a stable final equilibrium state exists, and the nonstationary components of the two-point functions of the anharmonic oscillator have negligible contributions to the power balance, we can show nonperturbatively that equilibration implies an FDR for the anharmonic oscillator. We then use a weakly anharmonic oscillator as an example to illustrate the validity of those two assumptions and show that in the weak anhamonicity limit, they are satisfied according to our first-order perturbative results..}, issn = {1550-7998}, doi = {10.1103/PhysRevD.101.125003}, author = {Hsiang, Jen-Tsung and Hu, Bei-Lok} } @article { ISI:000551007800002, title = {Fluctuations in Extractable Work Bound the Charging Power of Quantum Batteries}, journal = {Phys. Rev. Lett.}, volume = {125}, number = {4}, year = {2020}, month = {JUL 22}, pages = {040601}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study the connection between the charging power of quantum batteries and the fluctuations of the extractable work. We prove that in order to have a nonzero rate of change of the extractable work, the state rho(W) of the battery cannot be an eigenstatc of a {\textquoteleft}{\textquoteleft}free energy operator,{{\textquoteright}{\textquoteright}} defined by F H-W + beta(-1) log(rho(W)), where H-W is the Hamiltonian of the battery and beta is the inverse temperature of a reference thermal bath with respect to which the extractable work is calculated. We do so by proving that fluctuations in the free energy operator upper bound the charging power of a quantum battery. Our findings also suggest that quantum coherence in the battery enhances the charging process, which we illustrate on a toy model of a heat engine.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.125.040601}, author = {Pedro Garcia-Pintos, Luis and Hamma, Alioscia and del Campo, Adolfo} } @article {sau_anyons_2020, title = {From anyons to {Majoranas}}, journal = {Nat. Rev. Phys.}, volume = {2}, number = {12}, year = {2020}, note = {Place: CAMPUS, 4 CRINAN ST, LONDON, N1 9XW, ENGLAND Publisher: SPRINGERNATURE Type: Editorial Material}, month = {dec}, pages = {667{\textendash}668}, abstract = {Key advances Beam-splitter and interferometric measurements in the quantum Hall regime provide the strongest experimental proof to date of exotic anyonic particles. Individual states inside superconducting vortices, called Caroli-de Gennes-Matricon states, have been experimentally observed in low-density topological superconductors. Access to the Caroli-de Gennes-Matricon states provides a new platform in which anyonic particles may be braided and detected in three dimensional topological superconductors. Anyons, particles that are neither bosons nor fermions, were predicted in the 1980s, but strong experimental evidence for the existence of the simplest type of anyons has only emerged this year. Further theoretical and experimental advances promise to nail the existence of more exotic types of anyons, such as Majorana fermions, which would make topological quantum computation possible. Strong experimental evidence for the existence of the simplest type of anyons (particles that are neither bosons nor fermions) has emerged this year. The next step is to uncover more exotic types of anyons, such as Majorana fermions.

}, doi = {10.1038/s42254-020-00251-9}, author = {Sau, Jay and Simon, Steven and Vishveshwara, Smitha and Williams, James R.} } @article { ISI:000562277400001, title = {Frustration-induced supersolid phases of extended Bose-Hubbard model in the hard-core limit}, journal = {J. Phys.-Condes. Matter}, volume = {32}, number = {45}, year = {2020}, month = {OCT 28}, pages = {455401}, publisher = {IOP PUBLISHING LTD}, type = {Article}, abstract = {We investigate exotic supersolid phases in the extended Bose-Hubbard model with infinite projected entangled-pair state, numerical exact diagonalization, and mean-field theory. We demonstrate that many different supersolid phases can be generated by changing signs of hopping terms, and the interactions along with the frustration of hopping terms are important to stabilize those supersolid states. We argue the effect of frustration introduced by the competition of hopping terms in the supersolid phases from the mean-field point of view. This helps to give a clearer picture of the background mechanism for underlying superfluid/supersolid states to be formed. With this knowledge, we predict and realize thed-wave superfluid, which shares the same pairing symmetry with high-T(c)materials, and its extended phases. We believe that our results contribute to preliminary understanding for desired target phases in the real-world experimental systems.}, keywords = {Bose-Hubbard model, exact diagonalization, phase diagrams, projected entangled pair states, superfluids, supersolids}, issn = {0953-8984}, doi = {10.1088/1361-648X/aba383}, author = {Tu, Wei-Lin and Wu, Huan-Kuang and Suzuki, Takafumi} } @article {morita_full-dimensional_2020, title = {Full-dimensional quantum scattering calculations on ultracold atom-molecule collisions in magnetic fields: {The} role of molecular vibrations}, journal = {Phys. Rev. Res.}, volume = {2}, number = {4}, year = {2020}, note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article}, abstract = {{Rigorous quantum scattering calculations on ultracold molecular collisions in external fields present an outstanding computational problem due to strongly anisotropic atom-molecule interactions that depend on the relative orientation of the collision partners, as well as on their vibrational degrees of freedom. Here, we present the first numerically exact three-dimensional quantum scattering calculations on strongly anisotropic atom-molecule (Li + CaH) collisions in an external magnetic field based on the parity-adapted total angular momentum representation and a new three-dimensional potential energy surface for the triplet Li-CaH collision complex developed using the unrestricted coupled-cluster method with single, double, and perturbative triple excitations and a large quadruple-zeta-type basis set. We find that while the full three-dimensional treatment is necessary for the accurate description of cold Li(M-S = 1/2) + CaH(v = 0}, doi = {10.1103/PhysRevResearch.2.043294}, author = {Morita, Masato and Klos, Jacek and Tscherbul, V, Timur} } @article { ISI:000504435500005, title = {Ferromagnetism in quantum dot plaquettes}, journal = {Phys. Rev. B}, volume = {100}, number = {22}, year = {2019}, month = {DEC 23}, pages = {224421}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Following recent experimental progress concerning Nagaoka ferromagnetism in finite-size quantum dot plaquettes, a general theoretical analysis is warranted in order to ascertain in rather generic terms which arrangements of a small number of quantum dots can produce saturated ferromagnetic ground states and under which constraints on interaction and interdot tunneling in the plaquette. This is particularly necessary since Nagaoka ferromagnetism is fragile and arises only under rather special conditions. We test the robustness of ground state ferromagnetism in the presence of a long-range Coulomb interaction and long-range as well as short-range interdot hopping by modeling a wide range of different plaquette geometries accessible by arranging a few (similar to 4) quantum dots in a controlled manner. We find that ferromagnetism is robust to the presence of long-range Coulomb interactions, and we develop conditions constraining the tunneling strength such that the ground state is ferromagnetic. Additionally, we predict the presence of a partially spin-polarized ferromagnetic state for 4 electrons in a Y-shaped 4-quantum-dot plaquette. Finally, we consider 4 electrons in a ring of 5 dots. This does not satisfy the Nagaoka condition; however, we show that the ground state is spin 1 for strong, but not infinite, on-site interaction. Thus, even though Nagaoka{\textquoteright}s theorem does not apply, the ground state for the finite system with one hole in a ring of 5 dots is partially ferromagnetic. We provide detailed fully analytical results for the existence or not of ferromagnetic ground states in several quantum dot geometries which can be studied in currently available coupled quantum dot systems.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.100.224421}, author = {Buterakos, Donovan and Das Sarma, Sankar} } @article {ISI:000466889100001, title = {A fiber-integrated nanobeam single photon source emitting at telecom wavelengths}, journal = {Appl. Phys. Lett.}, volume = {114}, number = {17}, year = {2019}, month = {APR 29}, pages = {171101}, publisher = {AMER INST PHYSICS}, type = {Article}, abstract = {Fiber-coupled single photon sources are considered important components of photonics-based quantum information processors. Most fibercoupled single photon sources require careful alignment between fibers and quantum emitters. In this work, we present an alignment-free fiber-integrated single photon source based on an InAs/InP quantum dot emitting at telecom wavelengths. We designed a nanobeam containing the quantum dots attached to a fiber taper. The adiabatic tapered coupler of the nanobeam enables efficient light coupling to the fiber taper. Using a tungsten probe in a focused ion beam system, we transferred the nanobeam to the fiber taper. The observed fiber-coupled single photon emission occurs with a brightness of 1.4\% and a purity of 83\%. This device provides a building block for fiber-optic quantum circuits that have various applications, such as quantum communication and distributed quantum computing. Published under license by AIP Publishing.}, issn = {0003-6951}, doi = {10.1063/1.5089907}, author = {Lee, Chang-Min and Buyukkaya, Mustafa Atabey and Aghaeimeibodi, Shahriar and Karasahin, Aziz and Richardson, Christopher J. K. and Waks, Edo} } @conference {ISI:000482226300153, title = {First experimental steps toward an in situ gauge for direct measurement of relativistic intensities}, booktitle = {2019 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO)}, series = {Conference on Lasers and Electro-Optics}, year = {2019}, note = {Conference on Lasers and Electro-Optics (CLEO), San Jose, CA, MAY 05-10, 2019}, publisher = {IEEE; AdValue Photon; Amer Elements; Class5 Photon; Coherent; GoFoton; Light Convers; LightTrans; MKS; OZ Opt Online; Santec; ThorLabs; UQDevices; YSL Photon}, organization = {IEEE; AdValue Photon; Amer Elements; Class5 Photon; Coherent; GoFoton; Light Convers; LightTrans; MKS; OZ Opt Online; Santec; ThorLabs; UQDevices; YSL Photon}, type = {Proceedings Paper}, abstract = {Nearly 50 years ago Sarachik and Schappert suggested an intensity gauge based on wavelength shifts due to relativistic Thomson scattering. We present the first preliminary experimental results exploiting these shifts to make a direct measurement of peak intensities above 10(18) W/cm(2). (C) 2019 The Author(s)}, isbn = {978-1-943580-57-6}, issn = {2160-9020}, author = {Hill, III, W. T. and He, C. and Roso, L. and Perez-Hernandez, J. A. and Gatti, G. and de Marco, M. and Fedosejevs, R. and Longman, A.} } @article {ISI:000477908400014, title = {Fluctuation-dissipation and correlation-propagation relations from the nonequilibrium dynamics of detector-quantum field systems}, journal = {Phys. Rev. D}, volume = {100}, number = {2}, year = {2019}, month = {JUL 29}, pages = {025019}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We consider N uniformly accelerating Unruh-DeWitt detectors whose internal degrees of freedom are coupled to a massless scalar field in (1 + 1)D Minkowski space. We use the influence functional formalism to derive the Langevin equations governing the nonequilibrium dynamics of the internal degrees of freedom and show explicitly that the system relaxes in time and equilibrates. We also show that once the equilibrium condition is established a set of fluctuation-dissipation relations (FDRs) and correlation-propagation relations emerges for the detectors, extending earlier results of Raval, Hu, and Anglin {[}Stochastic theory of accelerated detectors in quantum fields, Phys. Rev. D 53, 7003 (1996)] which discovered these relations for the quantum field. Although similar in form to the FDRs commonly known from linear response theory, which assumes an equilibrium condition a priori, their physical connotations are dissimilar from that of a nonequilibrium origin. We show explicitly that both sets of relations are needed to guarantee the balance of energy flow in and out of the system in dynamical equilibrium with the field. These results are helpful to investigations of quantum information and communications of detectors in space experiments and inquiries of theoretical issues in black holes and cosmology.}, issn = {2470-0010}, doi = {10.1103/PhysRevD.100.025019}, author = {Hsiang, Jen-Tsung and Hu, B. L. and Lin, Shih-Yuin} } @article {ISI:000477924000099, title = {Fluctuation-dissipation and correlation-propagation relations in (1+3)D moving detector-quantum field systems}, journal = {Phys. Lett. B}, volume = {795}, year = {2019}, month = {AUG 10}, pages = {694-699}, publisher = {ELSEVIER}, type = {Article}, abstract = {The fluctuation-dissipation relations (FDR) are powerful relations which can capture the essence of the interplay between a system and its environment. Challenging problems of this nature which FDRs aid in our understanding include the backreaction of quantum field processes like particle creation on the spacetime dynamics in early universe cosmology or quantum black holes. The less familiar, yet equally important correlation-propagation relations (CPR) relate the correlations of stochastic forces on different detectors to the retarded and advanced parts of the radiation propagated in the field. Here, we analyze a system of N uniformly-accelerated Unruh-DeWitt detectors whose internal degrees of freedom (idf) are minimally coupled to a real, massless, scalar field in 4D Minkowski space, extending prior work in 2D with derivative coupling. Using the influence functional formalism, we derive the stochastic equations describing the nonequilibrium dynamics of the idfs. We show after the detector-field dynamics has reached equilibration the existence of the FDR and the CPR for the detectors, which combine to form a generalized fluctuation-dissipation matrix relation. We show explicitly the energy flows between the constituents of the system of detectors and between the system and the quantum field environment. This power balance anchors the generalized FDR. We anticipate this matrix relation to provide a useful guardrail in expounding some basic issues in relativistic quantum information, such as ensuring the self-consistency of the energy balance and tracking the quantum information transfer in the detector-field system. (C) 2019 The Authors. Published by Elsevier B.V.}, issn = {0370-2693}, doi = {10.1016/j.physletb.2019.06.062}, author = {Hsiang, Jen-Tsung and Hu, B. L. and Lin, Shih-Yuin and Yamamoto, Kazuhiro} } @article {14546, title = {Fluctuation-Induced Torque on a Topological Insulator out of Thermal Equilibrium}, journal = {Phys. Rev. Lett.}, volume = {123}, year = {2019}, month = {Aug}, pages = {055901}, doi = {10.1103/PhysRevLett.123.055901}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.123.055901}, author = {Maghrebi, M. F. and Gorshkov, A. V. and Sau, J. D.} } @article {ISI:000457058500007, title = {Fractional Josephson effect with and without Majorana zero modes}, journal = {Phys. Rev. B}, volume = {99}, number = {3}, year = {2019}, month = {JAN 29}, pages = {035312}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {It is known that the low-energy physics of the Josephson effect in the presence of Majorana zero modes exhibits a 4 pi periodicity as the Aharonov-Bohm flux varies in contrast to the 2 pi Josephson periodicity in usual superconducting junctions. We study this fractional Josephson effect in one-dimensional topological superconductors in Majorana nanowire systems by focusing on the features of the phase-energy relations in a superconducting semiconductor nanowire with spin-orbital coupling by including different factors operational in experimental systems, such as short wire length, suppression of superconducting gap, and the presence of an Andreev bound state. We show that even in the absence of the Majorana zero modes, some nontopological physical effects can manifest a 4 pi periodicity of the phase-energy relation in the Josephson junction, thus providing an alternative physics for fractional Josephson effect with no underlying Majorana zero modes. Furthermore, we consider several scenarios of inhomogeneous chemical potential distributions in the superconducting nanowire leading to four Majorana bound states and construct the effective four-Majorana model to correctly describe the low-energy theory of the Josephson effect. In this setup, multiple Majorana zero modes can also have the 4 pi fractional Josephson effect, although the underlying physics arises from Andreev bound states since two close-by Majorana bound states effectively form Andreev bound states. Our work demonstrates that the mere observation of a fractional Josephson effect simulating 4 pi periodicity might not, by itself, be taken as the definitive evidence for topological superconductivity. This finding has important implications for the ongoing search for non-Abelian Majorana zero modes and efforts for developing topological qubits.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.99.035312}, author = {Chiu, Ching-Kai and S. Das Sarma} } @article {ISI:000482940400006, title = {Frequency shifts due to Stark effects on a rubidium two-photon transition}, journal = {Phys. Rev. A}, volume = {100}, number = {2}, year = {2019}, month = {AUG 28}, pages = {023417}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The 5S(1/2) -> 5D(5/2) two-photon transition in Rb is of interest for the development of a compact optical atomic clock. Here we present a rigorous calculation of the 778.1-nm ac Stark shift {[}2.30(4) x 10(-13)(mW/mm(2))(-1)] that is in good agreement with our measured value of 2.5(2) x 10(-13)(mW/mm(2))(-1). We include a calculation of the temperature-dependent blackbody radiation (BBR) shift, and we predict that the clock could be operated either with zero net BBR shift {[}T = 495.9(27) K] or with zero first-order sensitivity {[}T = 368.1(14) K]. Also described is the calculation of the dc Stark shift of 5.5(1) x 10(-15)/(V/cm(2)) as well as clock sensitivities to optical alignment variations in both a cat{\textquoteright}s eye and a flat mirror retroreflector. Finally, we characterize these Stark effects, discussing mitigation techniques necessary to reduce final clock instabilities.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.023417}, author = {Martin, Kyle W. and Stuhl, Benjamin and Eugenio, Jon and Safronova, Marianna S. and Phelps, Gretchen and Burke, John H. and Lemke, Nathan D.} } @article { ISI:000446554000001, title = {Failure of Kohn{\textquoteright}s theorem and the apparent failure of the f-sum rule in intrinsic Dirac-Weyl materials in the presence of a filled Fermi sea}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {15}, year = {2018}, month = {OCT 5}, pages = {155112}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.155112}, author = {Throckmorton, Robert E. and S. Das Sarma} } @article { ISI:000439411700003, title = {Ferromagnetism and Wigner crystallization in kagome graphene and related structures}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {3}, year = {2018}, month = {JUL 23}, pages = {035135}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.035135}, author = {Chen, Yuanping and Xu, Shenglong and Xie, Yuee and Zhong, Chengyong and Wu, Congjun and Zhang, S. B.} } @article { ISI:000439974200006, title = {Fingerprints of Berry phases in the bulk exciton spectrum of a topological insulator}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {4}, year = {2018}, month = {JUL 27}, pages = {045430}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.045430}, author = {Allocca, Andrew A. and Efimkin, Dmitry K. and Galitski, Victor M.} } @article { ISI:000433040400001, title = {Floquet Supersymmetry}, journal = {PHYSICAL REVIEW LETTERS}, volume = {120}, number = {21}, year = {2018}, month = {MAY 24}, pages = {210603}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.120.210603}, author = {Iadecola, Thomas and Hsieh, Timothy H.} } @article { ISI:000426845500044, title = {Fractal universality in near-threshold magnetic lanthanide dimers}, journal = {SCIENCE ADVANCES}, volume = {4}, number = {2}, year = {2018}, month = {FEB}, pages = {UNSP eaap8308}, issn = {2375-2548}, doi = {10.1126/sciadv.aap8308}, author = {Makrides, Constantinos and Li, Ming and Tiesinga, Eite and Kotochigova, Svetlana} } @article { ISI:000448933900006, title = {Fractional Quantum Hall Effect at nu=2+6/13: The Parton Paradigm for the Second Landau Level}, journal = {PHYSICAL REVIEW LETTERS}, volume = {121}, number = {18}, year = {2018}, month = {NOV 1}, pages = {186601}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.121.186601}, author = {Balram, Ajit C. and Mukherjee, Sutirtha and Park, Kwon and Barkeshli, Maissam and Rudner, Mark S. and Jain, J. K.} } @article {10546, title = {Fractional Quantum Hall Phases of Bosons with Tunable Interactions: From the Laughlin Liquid to a Fractional Wigner Crystal}, journal = {Phys. Rev. Lett.}, volume = {121}, year = {2018}, month = {Dec}, pages = {253403}, doi = {10.1103/PhysRevLett.121.253403}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.121.253403}, author = {Gra{\ss}, Tobias and Bienias, Przemyslaw and Gullans, Michael J. and Lundgren, Rex and Maciejko, Joseph and Gorshkov, Alexey V.} } @article { ISI:000415568700001, title = {Fast pulse sequences for dynamically corrected gates in singlet-triplet qubits}, journal = {PHYSICAL REVIEW B}, volume = {96}, number = {19}, year = {2017}, month = {NOV 17}, issn = {2469-9950}, doi = {10.1103/PhysRevB.96.195424}, author = {Throckmorton, Robert E. and Zhang, Chengxian and Yang, Xu-Chen and Wang, Xin and Barnes, Edwin and S. Das Sarma} } @article { ISI:000413663300001, title = {Fast Quantum State Transfer and Entanglement Renormalization Using Long-Range Interactions}, journal = {PHYSICAL REVIEW LETTERS}, volume = {119}, number = {17}, year = {2017}, month = {OCT 25}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.119.170503}, author = {Eldredge, Zachary and Gong, Zhe-Xuan and Young, Jeremy T. and Moosavian, Ali Hamed and Foss-Feig, Michael and Gorshkov, Alexey V.} } @article {7741, title = {Fault-tolerant quantum error detection}, journal = {Science Advances}, volume = {3}, year = {2017}, abstract = {Quantum computers will eventually reach a size at which quantum error correction becomes imperative. Quantum information can be protected from qubit imperfections and flawed control operations by encoding a single logical qubit in multiple physical qubits. This redundancy allows the extraction of error syndromes and the subsequent detection or correction of errors without destroying the logical state itself through direct measurement. We show the encoding and syndrome measurement of a fault-tolerantly prepared logical qubit via an error detection protocol on four physical qubits, represented by trapped atomic ions. This demonstrates the robustness of a logical qubit to imperfections in the very operations used to encode it. The advantage persists in the face of large added error rates and experimental calibration errors.

}, doi = {10.1126/sciadv.1701074}, url = {http://advances.sciencemag.org/content/3/10/e1701074}, author = {Linke, Norbert M. and Gutierrez, Mauricio and Landsman, Kevin A. and Figgatt, Caroline and Debnath, Shantanu and Brown, Kenneth R. and Monroe, Christopher} } @article { ISI:000379647900004, title = {Fast control of semiconductor qubits beyond the rotating-wave approximation}, journal = {PHYSICAL REVIEW A}, volume = {94}, number = {1}, year = {2016}, month = {JUL 14}, issn = {2469-9926}, doi = {10.1103/PhysRevA.94.012321}, author = {Song, Yang and Kestner, J. P. and Wang, Xin and S. Das Sarma} } @article { ISI:000372413000004, title = {Filter function formalism beyond pure dephasing and non-Markovian noise in singlet-triplet qubits}, journal = {PHYSICAL REVIEW B}, volume = {93}, number = {12}, year = {2016}, month = {MAR 16}, issn = {2469-9950}, doi = {10.1103/PhysRevB.93.121407}, author = {Barnes, Edwin and Rudner, Mark S. and Martins, Frederico and Malinowski, Filip K. and Marcus, Charles M. and Kuemmeth, Ferdinand} } @article {ISI:000369217400001, title = {Flight of a heavy particle nonlinearly coupled to a quantum bath}, journal = {PHYSICAL REVIEW B}, volume = {93}, number = {1}, year = {2016}, month = {JAN 28}, pages = {014309}, abstract = {Fluctuation and dissipation are byproducts of coupling to the {\textquoteleft}{\textquoteleft}environment.{{\textquoteright}{\textquoteright}} The Caldeira-Leggett model, a successful paradigm of quantum Brownian motion, views the environment as a collection of harmonic oscillators linearly coupled to the system. However, symmetry considerations may forbid a linear coupling, e.g., for a neutral particle in quantum electrodynamics. We argue that the absence of linear couplings can lead to a fundamentally different behavior. Specifically, we consider a heavy particle quadratically coupled to quantum fluctuations of the bath. In one dimension the particle undergoes anomalous diffusion, unfolding as a power-law distribution in space, reminiscent of Levy flights. We suggest condensed matter analogs where similar effects may arise.}, issn = {2469-9950}, doi = {10.1103/PhysRevB.93.014309}, author = {Maghrebi, Mohammad F. and Krueger, Matthias and Kardar, Mehran} } @article { ISI:000369727700005, title = {Formalism for the solution of quadratic Hamiltonians with large cosine terms}, journal = {PHYSICAL REVIEW B}, volume = {93}, number = {7}, year = {2016}, month = {FEB 8}, issn = {2469-9950}, doi = {10.1103/PhysRevB.93.075118}, author = {Ganeshan, Sriram and Levin, Michael} } @article {ISI:000372360400001, title = {Feshbach enhanced s-wave scattering of fermions: direct observation with optimized absorption imaging}, journal = {NEW JOURNAL OF PHYSICS}, volume = {18}, year = {2015}, month = {DEC 17}, pages = {013001}, issn = {1367-2630}, doi = {10.1088/1367-2630/18/1/013001}, author = {Genkina, D. and Aycock, L. M. and Stuhl, B. K. and Lu, H-I and Williams, R. A. and Ian B Spielman} } @article { ISI:000360655900016, title = {Formation of strain-induced quantum dots in gated semiconductor nanostructures}, journal = {AIP ADVANCES}, volume = {5}, number = {8}, year = {2015}, month = {AUG}, issn = {2158-3226}, doi = {10.1063/1.4928320}, author = {Thorbeck, Ted and Zimmerman, Neil M.} } @article { ISI:000352058600004, title = {Fractional quantum Hall states of Rydberg polaritons}, journal = {PHYSICAL REVIEW A}, volume = {91}, number = {3}, year = {2015}, month = {MAR 31}, pages = {033838}, issn = {1050-2947}, doi = {10.1103/PhysRevA.91.033838}, author = {Maghrebi, Mohammad F. and Yao, Norman Y. and Hafezi, Mohammad and Pohl, Thomas and Firstenberg, Ofer and Gorshkov, Alexey V.} } @article { ISI:000351634800008, title = {From membrane-in-the-middle to mirror-in-the-middle with a high-reflectivity sub-wavelength grating}, journal = {ANNALEN DER PHYSIK}, volume = {527}, number = {1-2, SI}, year = {2015}, month = {JAN}, pages = {81-88}, issn = {0003-3804}, doi = {10.1002/andp.201400142}, author = {Stambaugh, Corey and Xu, Haitan and Kemiktarak, Utku and Taylor, Jacob and Lawall, John} } @article { ISI:000348513500057, title = {Fabrication of Uniform Nanoscale Cavities via Silicon Direct Wafer Bonding}, journal = {JOVE-JOURNAL OF VISUALIZED EXPERIMENTS}, number = {83}, year = {2014}, month = {JAN}, issn = {1940-087X}, doi = {10.3791/51179}, author = {Thomson, Stephen R. D. and Perron, Justin K. and Kimball, Mark O. and Mehta, Sarabjit and Gasparini, Francis M.} } @article { ISI:000354864200003, title = {Fast and highly resolved capture of the joint spectral density of photon pairs}, journal = {OPTICA}, volume = {1}, number = {5}, year = {2014}, month = {NOV 20}, pages = {281-284}, issn = {2334-2536}, doi = {10.1364/OPTICA.1.000281}, author = {Fang, Bin and Cohen, Offir and Liscidini, Marco and Sipe, John E. and Lorenz, Virginia O.} } @article { ISI:000332852200011, title = {Fermion-mediated long-range interactions between bosons stored in an optical lattice}, journal = {APPLIED PHYSICS B-LASERS AND OPTICS}, volume = {114}, number = {4}, year = {2014}, month = {MAR}, pages = {527-536}, issn = {0946-2171}, doi = {10.1007/s00340-013-5556-5}, author = {Subhadeep De and Ian B Spielman} } @article { ISI:000333559400002, title = {Ferromagnetic response of a {\textquoteleft}{\textquoteleft}high-temperature{{\textquoteright}{\textquoteright}} quantum antiferromagnet}, journal = {PHYSICAL REVIEW B}, volume = {89}, number = {12}, year = {2014}, month = {MAR 31}, pages = {121118}, issn = {1098-0121}, doi = {10.1103/PhysRevB.89.121118}, author = {Wang, Xin and Sensarma, Rajdeep and S. Das Sarma} } @article { ISI:000336355200007, title = {From atoms to steps: The microscopic origins of crystal evolution}, journal = {SURFACE SCIENCE}, volume = {625}, year = {2014}, month = {JUL}, pages = {37-43}, issn = {0039-6028}, doi = {10.1016/j.susc.2014.02.015}, author = {Patrone, Paul N. and Einstein, T. L. and Margetis, Dionisios} } @article { ISI:000346376500004, title = {Frustration and multicriticality in the antiferromagnetic spin-1 chain}, journal = {PHYSICAL REVIEW B}, volume = {90}, number = {21}, year = {2014}, month = {DEC 15}, issn = {1098-0121}, doi = {10.1103/PhysRevB.90.214426}, author = {Pixley, J. H. and Shashi, Aditya and Nevidomskyy, Andriy H.} } @article { ISI:000316816200013, title = {Fabrication and Electrical Characterization of Fully CMOS-Compatible Si Single-Electron Devices}, journal = {IEEE TRANSACTIONS ON ELECTRON DEVICES}, volume = {60}, number = {1}, year = {2013}, month = {JAN}, pages = {78-83}, issn = {0018-9383}, doi = {10.1109/TED.2012.2227322}, author = {Koppinen, P. J. and Stewart, Jr., M. D. and Zimmerman, Neil M.} } @article { ISI:000323241000077, title = {Fabrication of Nanoassemblies Using Flow Control}, journal = {Nano Lett.}, volume = {13}, number = {8}, year = {2013}, month = {AUG}, pages = {3936}, issn = {1530-6984}, doi = {10.1021/nl402059u}, author = {Ropp, Chad and Cummins, Zachary and Nah, Sanghee and Qin, Sijia and Seog, Ji Hyun and Lee, Sang Bok and John T Fourkas and Shapiro, Benjamin and Edo Waks} } @conference { ISI:000326980500015, title = {Feedback in a cavity QED system for control of quantum beats}, booktitle = {ICAP 2012 - 23RD INTERNATIONAL CONFERENCE ON ATOMIC PHYSICS}, series = {EPJ Web of Conferences}, volume = {57}, year = {2013}, note = {23rd International Conference on Atomic Physics (ICAP), Ecole Polytechnique, FRANCE, JUL 23-27, 2012}, issn = {2100-014X}, doi = {10.1051/epjconf/20135703005}, author = {Cimmarusti, A. D. and Patterson, B. D. and Schroeder, C. A. and Orozco, L. A. and Barberis-Blostein, P. and Carmichael, H. J.}, editor = {Dulieu, O and Grangier, P and Leduc, M and Perrin, H} } @article { ISI:000316660000012, title = {Feshbach resonances, weakly bound molecular states, and coupled-channel potentials for cesium at high magnetic fields}, journal = {Phys. Rev. A}, volume = {87}, number = {3}, year = {2013}, month = {MAR 25}, issn = {1050-2947}, doi = {10.1103/PhysRevA.87.032517}, author = {Martin Berninger and Alessandro Zenesini and Bo Huang and Walter Harm and Naegerl, Hanns-Christoph and Francesca Ferlaino and Rudolf Grimm and Paul S Julienne and Jeremy M Hutson} } @article { ISI:000313422800001, title = {Feshbach spectroscopy of an ultracold mixture of Rb-85 and Cs-133}, journal = {Phys. Rev. A}, volume = {87}, number = {1}, year = {2013}, month = {JAN 11}, issn = {1050-2947}, doi = {10.1103/PhysRevA.87.010703}, author = {Cho, Hung-Wen and McCarron, Daniel J. and Koeppinger, Michael P. and Jenkin, Daniel L. and Butler, Kirsteen L. and Paul S Julienne and Blackley, Caroline L. and Le Sueur, C. Ruth and Jeremy M Hutson and Cornish, Simon L.} } @article { ISI:000314683100005, title = {Finite temperature inelastic mean free path and quasiparticle lifetime in graphene}, journal = {Phys. Rev. B}, volume = {87}, number = {8}, year = {2013}, month = {FEB 5}, issn = {1098-0121}, doi = {10.1103/PhysRevB.87.085406}, author = {Li, Qiuzi and S. Das Sarma} } @article { ISI:000317584800011, title = {Finite-momentum dimer bound state in a spin-orbit-coupled Fermi gas}, journal = {PHYSICAL REVIEW A}, volume = {87}, number = {4}, year = {2013}, month = {APR 12}, issn = {1050-2947}, doi = {10.1103/PhysRevA.87.043616}, author = {Dong, Lin and Jiang, Lei and Hu, Hui and Pu, Han} } @article { ISI:000324234700005, title = {Formation and decay of Bose-Einstein condensates in an excited band of a double-well optical lattice}, journal = {Phys. Rev. A}, volume = {88}, number = {3}, year = {2013}, month = {SEP 12}, pages = {033615}, issn = {1050-2947}, doi = {10.1103/PhysRevA.88.033615}, author = {Paul, Saurabh and Eite Tiesinga} } @article { ISI:000321945200001, title = {Fulde-Ferrell pairing instability in spin-orbit coupled Fermi gas}, journal = {NEW JOURNAL OF PHYSICS}, volume = {15}, year = {2013}, month = {JUL 17}, issn = {1367-2630}, doi = {10.1088/1367-2630/15/7/075014}, author = {Dong, Lin and Jiang, Lei and Pu, Han} } @article {ISI:000312486600004, title = {Flux lattices reformulated}, journal = {New J. Phys.}, volume = {14}, year = {2012}, pages = {123022}, keywords = {Single Fellow}, issn = {1367-2630}, doi = {10.1088/1367-2630/14/12/123022}, author = {Gediminas Juzeliunas and Ian B Spielman} } @article {Baltrusch2011, title = {Fast and robust quantum computation with ionic Wigner crystals}, journal = {Phys. Rev. A}, volume = {83}, number = {4}, year = {2011}, month = {apr}, pages = {042319}, keywords = {2011}, issn = {1050-2947}, url = {http://pra.aps.org/abstract/PRA/v83/i4/e042319}, author = {Baltrusch, J. and Negretti, A. and Jacob M Taylor and Tommaso Calarco} } @article {Lindner2011, title = {Floquet topological insulator in semiconductor quantum wells}, journal = {Nat. Phys.}, volume = {7}, number = {6}, year = {2011}, month = {mar}, pages = {490{\textendash}495}, publisher = {Nature Publishing Group}, keywords = {2011, Single Fellow}, issn = {1745-2473}, doi = {10.1038/nphys1926}, author = {Lindner, Netanel H. and Refael, Gil and Victor M Galitski} } @article {2457, title = {Fractional quantum Hall effect in the absence of Landau levels}, journal = {Nature Communications}, volume = {2}, year = {2011}, month = {7/2011}, pages = {389}, doi = {10.1038/ncomms1380}, author = {Dong Sheng and Zheng-Cheng Gu and Kai Sun and L. Sheng} } @article {Chen2011, title = {Frequency-bin entangled comb of photon pairs from a Silicon-on-Insulator micro-resonator}, journal = {Optics Express}, volume = {19}, number = {2}, year = {2011}, month = {jan}, pages = {1470}, publisher = {OSA}, abstract = {We present a quantum-mechanical theory to describe narrowband photon-pair generation via four-wave mixing in a Silicon-on-Insulator (SOI) micro-resonator. We also provide design principles for efficient photon-pair generation in an SOI micro-resonator through extensive numerical simulations. Microring cavities are shown to have a much wider dispersion-compensated frequency range than straight cavities. A microring with an inner radius of 8 $μ$m can output an entangled photon comb of 21 pairwise-correlated peaks (42 comb lines) spanning from 1.3 $μ$m to 1.8 $μ$m. Such on-chip quantum photonic devices offer a path toward future integrated quantum photonics and quantum integrated circuits.

}, keywords = {2011, four-wave mixing, integrated optics, Micro-optical devices, Nonlinear optics, Quantum information and processing, Resonators, Single Fellow}, issn = {1094-4087}, url = {http://www.opticsexpress.org/abstract.cfm?URI=oe-19-2-1470}, author = {Jun Chen and Zachary H Levine and Jingyun Fan and Alan L Migdall} } @article {Galitski2010, title = {Fermionization transform for certain higher-dimensional quantum spin models}, journal = {Phys. Rev. B}, volume = {82}, number = {6}, year = {2010}, month = {aug}, pages = {060411}, keywords = {2010, Single Fellow}, issn = {1098-0121}, url = {http://prb.aps.org/abstract/PRB/v82/i6/e060411}, author = {Victor M Galitski} } @article {Chin2010, title = {Feshbach resonances in ultracold gases}, journal = {Rev. Mod. Phys.}, volume = {82}, number = {2}, year = {2010}, month = {apr}, pages = {1225{\textendash}1286}, keywords = {2010}, issn = {0034-6861}, url = {http://rmp.aps.org/abstract/RMP/v82/i2/p1225_1}, author = {Chin, Cheng and Paul S Julienne and Eite Tiesinga} } @article { ISI:000286768100007, title = {Fractional quantum Hall effects in bilayers in the presence of interlayer tunneling and charge imbalance}, journal = {PHYSICAL REVIEW B}, volume = {82}, number = {23}, year = {2010}, month = {DEC 9}, issn = {1098-0121}, doi = {10.1103/PhysRevB.82.235312}, author = {Peterson, Michael R. and Papic, Z. and S. Das Sarma} } @article { ISI:000274664500043, title = {Fractional Quantum Hall State at nu=5/2 and the Moore-Read Pfaffian}, journal = {PHYSICAL REVIEW LETTERS}, volume = {104}, number = {7}, year = {2010}, month = {FEB 19}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.104.076803}, author = {Storni, M. and Morf, R. H. and S. Das Sarma} } @article {Barberis-Blostein2010, title = {From quantum feedback to probabilistic error correction: manipulation of quantum beats in cavity QED}, journal = {New J. Phys.}, volume = {12}, number = {2}, year = {2010}, month = {feb}, pages = {023002}, abstract = {It is shown how one can implement quantum feedback and probabilistic error correction in an open quantum system consisting of a single atom, with ground- and excited-state Zeeman structure, in a driven two-mode optical cavity. The ground-state superposition is manipulated and controlled through conditional measurements and external fields, which shield the coherence and correct quantum errors. Modeling an experimentally realistic situation demonstrates the robustness of the proposal for realization in the laboratory.}, keywords = {2010}, issn = {1367-2630}, url = {http://stacks.iop.org/1367-2630/12/i=2/a=023002}, author = {P Barberis-Blostein and Norris, D G and Luis A Orozco and Howard J Carmichael} } @article {Lee2010, title = {F-wave pairing of cold atoms in optical lattices}, journal = {Phys. Rev. A}, volume = {82}, number = {5}, year = {2010}, month = {nov}, keywords = {2010, Single Fellow}, issn = {1050-2947}, url = {http://pra.aps.org/abstract/PRA/v82/i5/e053611}, author = {Lee, Wei-Cheng and Wu, Congjun and S. Das Sarma} } @article {2465, title = {Field-sensitive addressing and control of field-insensitive neutral-atom qubits}, journal = {Nature Physics}, volume = {5}, year = {2009}, month = {7/2009}, pages = {575-580}, doi = {10.1038/nphys1330}, author = {Lundblad, N. and J. M. Obrecht and Ian B Spielman and J V Porto} } @article { ISI:000263815400088, title = {Fluctuation-induced first-order transition in p-wave superconductors}, journal = {PHYSICAL REVIEW B}, volume = {79}, number = {5}, year = {2009}, month = {FEB}, issn = {1098-0121}, doi = {10.1103/PhysRevB.79.054514}, author = {Li, Qi and Belitz, D. and Toner, John} } @article {Willis2009, title = {Four-wave mixing in the diamond configuration in an atomic vapor}, journal = {Phys. Rev. A}, volume = {79}, number = {3}, year = {2009}, month = {mar}, keywords = {2009}, issn = {1050-2947}, url = {http://pra.aps.org/abstract/PRA/v79/i3/e033814}, author = {R T Willis and Francisco E Becerra and Luis A Orozco and Steven L Rolston} } @article {Lutchyn2009a, title = {Frequency and temperature dependence of the anomalous ac Hall conductivity in a chiral px+ipy superconductor with impurities}, journal = {Phys. Rev. B}, volume = {80}, number = {10}, year = {2009}, month = {sep}, keywords = {2009, Single Fellow}, issn = {1098-0121}, url = {http://prb.aps.org/abstract/PRB/v80/i10/e104508}, author = {Roman M Lutchyn and Nagornykh, Pavel and Victor M Yakovenko} } @article { ISI:000257424700054, title = {Finite-layer thickness stabilizes the Pfaffian state for the 5/2 fractional quantum Hall effect: Wave function overlap and topological degeneracy}, journal = {PHYSICAL REVIEW LETTERS}, volume = {101}, number = {1}, year = {2008}, month = {JUL 4}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.101.016807}, author = {Peterson, Michael. R. and Jolicoeur, Th. and S. Das Sarma} } @article {Khodel2008, title = {Flattening of single-particle spectra in strongly correlated electron systems and the violation of the Wiedemann-Franz law}, journal = {JETP Letters}, volume = {86}, number = {12}, year = {2008}, month = {feb}, pages = {772{\textendash}778}, abstract = {The renormalization of the Wiedemann-Franz (WF) ratio in strongly correlated electron systems is analyzed within the Landau quasiparticle picture. We demonstrate that the WF law is violated: (i) at the quantum critical point, where the effective mass diverges, and (ii) beyond a point of fermion condensation, where the single-particle spectrum \$\backslash epsilon(p)\$ becomes flat. Results of the analysis are compared with available experimental data.}, keywords = {2008, Single Fellow}, issn = {0021-3640}, url = {http://arxiv.org/abs/0711.3777}, author = {V A Khodel and Victor M Yakovenko and M V Zverev} } @article {Wu2007, title = {Flat Bands and Wigner Crystallization in the Honeycomb Optical Lattice}, journal = {Phys. Rev. Lett.}, volume = {99}, number = {7}, year = {2007}, month = {aug}, keywords = {2007, Single Fellow}, issn = {0031-9007}, url = {http://prl.aps.org/abstract/PRL/v99/i7/e070401}, author = {Wu, Congjun and Doron L. Bergman and Balents, Leon and S. Das Sarma} } @article {Safronova2006, title = {Frequency-dependent polarizabilities of alkali-metal atoms from ultraviolet through infrared spectral regions}, journal = {Phys. Rev. A}, volume = {73}, number = {2}, year = {2006}, month = {feb}, keywords = {2006, Single Fellow}, issn = {1050-2947}, url = {http://pra.aps.org/abstract/PRA/v73/i2/e022505}, author = {Marianna S Safronova and Arora, Bindiya and Charles W Clark} }