Quantum systems are promising candidates for sensing of weak signals as they can be highly sensitive to external perturbations, thus providing excellent performance when estimating parameters of external fields. However, when trying to detect weak signals that are hidden by background noise, the signal-to-noise ratio is a more relevant metric than raw sensitivity. We identify, under modest assumptions about the statistical properties of the signal and noise, the optimal quantum control to detect an external signal in the presence of background noise using a quantum sensor. Interestingly, for white background noise, the optimal solution is the simple and well-known spin-locking control scheme. Using numerical techniques, we further generalize these results to the case of background noise with a Lorentzian spectrum. We show that for increasing correlation time, pulse based sequences, such as CPMG, are also close to the optimal control for detecting the signal, with the crossover dependent on the signal frequency. These results show that an optimal detection scheme can be easily implemented in near-term quantum sensors without the need for complicated pulse shaping.

}, doi = {10.1038/s41534-021-00383-5}, url = {https://doi.org/10.1038/s41534-021-00383-5}, author = {Paraj Titum and Kevin Schultz and Alireza Seif and Gregory Quiroz and B. D. Clader} } @article { WOS:000646067200012, title = {Optimal measurement of field properties with quantum sensor networks}, journal = {Phys. Rev. A}, volume = {103}, number = {3}, year = {2021}, month = {MAR 29}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We consider a quantum sensor network of qubit sensors coupled to a field f (x; theta) analytically parameterized by the vector of parameters theta. The qubit sensors are fixed at positions x(1), ..., x(d). While the functional form of f (x; theta) is known, the parameters theta are not. We derive saturable bounds on the precision of measuring an arbitrary analytic function q(theta) of these parameters and construct the optimal protocols that achieve these bounds. Our results are obtained from a combination of techniques from quantum information theory and duality theorems for linear programming. They can be applied to many problems, including optimal placement of quantum sensors, field interpolation, and the measurement of functionals of parametrized fields.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.103.L030601}, author = {Qian, Timothy and Bringewatt, Jacob and Boettcher, Igor and Bienias, Przemyslaw and Gorshkov, V, Alexey} } @article { WOS:000643598200024, title = {Quantum Matched Filtering-Signal Processing in the Quantum Age}, journal = {Johns Hopkins APL Tech. Dig.}, volume = {35}, number = {4}, year = {2021}, pages = {422-425}, publisher = {JOHNS HOPKINS UNIV APPLIED PHYSICS LABORATORY LLC}, type = {Article}, abstract = {Optimal quantum control theory identifies the quantum equivalent of a matched filter, which maximizes the signal-to-noise ratio, enabling exploitation of extremely high sensitivity of quantum sensors to detect known signals of interest. This article describes a Johns Hopkins University Applied Physics Laboratory (APL) team{\textquoteright}s work in this field.}, issn = {0270-5214}, author = {Titum, Paraj and Schultz, Kevin M. and Seif, Alireza and Quiroz, Gregory D. and Clader, B. David} } @article { ISI:000491132700014, title = {Demonstration of slow light in rubidium vapor using single photons from a trapped ion}, journal = {Sci. Adv.}, volume = {5}, number = {10}, year = {2019}, month = {OCT}, pages = {eaav4651}, publisher = {AMER ASSOC ADVANCEMENT SCIENCE}, type = {Article}, abstract = {Practical implementation of quantum networks is likely to interface different types of quantum systems. Photonically linked hybrid systems, combining unique properties of each constituent system, have typically required sources with the same photon emission wavelength. Trapped ions and neutral atoms both have compelling properties as nodes and memories in a quantum network but have never been photonically linked because of vastly different operating wavelengths. Here, we demonstrate the first interaction between neutral atoms and photons emitted from a single trapped ion. We use slow light in Rb-87 vapor to delay photons originating from a trapped Ba-138(+) ion by up to 13.5 +/- 0.5 ns, using quantum frequency conversion to overcome the frequency difference between the ion and neutral atoms. The delay is tunable and preserves the temporal profile of the photons. This result showcases a hybrid photonic interface usable as a synchronization tool-a critical component in any future large-scale quantum network.}, issn = {2375-2548}, doi = {10.1126/sciadv.aav4651}, author = {Siverns, J. D. and Hannegan, J. and Quraishi, Q.} } @article {ISI:000466037000001, title = {Dynamical Hamiltonian engineering of 2D rectangular lattices in a one-dimensional ion chain}, journal = {npj Quantum Inform.}, volume = {5}, year = {2019}, month = {APR 26}, pages = {32}, publisher = {SPRINGERNATURE}, type = {Article}, abstract = {Controlling the interaction graph between spins or qubits in a quantum simulator allows user-controlled tailoring of native interactions to achieve a target Hamiltonian. Engineering long-ranged phonon-mediated spin-spin interactions in a trapped ion quantum simulator offers such a possibility. Trapped ions, a leading candidate for quantum simulation, are most readily trapped in a linear 1D chain, limiting their utility for readily simulating higher dimensional spin models. In this work, we introduce a hybrid method of analog-digital simulation for simulating 2D spin models which allows for the dynamic changing of interactions to achieve a new graph using a linear 1D chain. We focus this numerical work on engineering 2D rectangular nearest-neighbor spin lattices, demonstrating that the required control parameters scale linearly with ion number. This hybrid approach offers compelling possibilities for the use of 1D chains in the study of Hamiltonian quenches, dynamical phase transitions, and quantum transport in 2D and 3D.}, doi = {10.1038/s41534-019-0147-x}, author = {Rajabi, Fereshteh and Motlakunta, Sainath and Shih, Chung-You and Kotibhaskar, Nikhil and Quraishi, Qudsia and Ajoy, Ashok and Islam, Rajibul} } @article {ISI:000460648100005, title = {Electric dipole matrix elements for the 6p(2)P(J) -> 7s(2)S(1/2) transition in atomic cesium}, journal = {Phys. Rev. A}, volume = {99}, number = {3}, year = {2019}, month = {MAR 5}, pages = {032504}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We report a measurement of the ratio of electric dipole transition matrix elements of cesium for the 6p(2)P(1/2) -> 7s(2)S(1/2) and 6p(2)P(3/2) -> 7s(2)S(1/2 )transitions. We determine this ratio of matrix elements through comparisons of two-color, two-photon excitation rates of the 7s(2)S(1/2) state using laser beams with polarizations parallel to one another vs perpendicular to one another. Our result of R < 7s(2)S(1/2)parallel to r parallel to 6P(2)P(3/2)>/< 7s(2)S(1/2)parallel to r parallel to 6P(2)P(1/2)> = 1.5272(17) is in excellent agreement with a theoretical prediction of R = 1.5270(27). Moreover, the accuracy of the experimental ratio is sufficiently high to differentiate between various theoretical approaches. To our knowledge, there are no prior experimental measurements of R. Combined with our recent determination of the lifetime of the 7s(2)S(1/2) state, we determine reduced matrix elements for these two transitions, < 7s(2)S(1/2)parallel to r parallel to 6P(2)P(3/2)> = -6.489(5)a(0) and < 7s(2)S(1/2)parallel to r parallel to 6P(2)P(1/2 >) = -4.249(4)a(0). These matrix elements are also in excellent agreement with theoretical calculations. These measurements improve knowledge of Cs properties needed for parity violation studies and provide benchmarks for tests of high-precision theory.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.032504}, author = {Toh, George and Damitz, Amy and Glotzbach, Nathan and Quirk, Jonah and Stevenson, I. C. and Choi, J. and Safronova, M. S. and Elliott, D. S.} } @article { ISI:000489036000001, title = {Heisenberg-scaling measurement protocol for analytic functions with quantum sensor networks}, journal = {Phys. Rev. A}, volume = {100}, number = {4}, year = {2019}, month = {OCT 7}, pages = {042304}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We generalize past work on quantum sensor networks to show that, for d input parameters, entanglement can yield a factor O(d) improvement in mean-squared error when estimating an analytic function of these parameters. We show that the protocol is optimal for qubit sensors, and we conjecture an optimal protocol for photons passing through interferometers. Our protocol is also applicable to continuous variable measurements, such as one quadrature of a field operator. We outline a few potential applications, including calibration of laser operations in trapped ion quantum computing.}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.042304}, author = {Qian, Kevin and Eldredge, Zachary and Ge, Wenchao and Pagano, Guido and Monroe, Christopher and Porto, V, J. and Gorshkov, V, Alexey} } @article {ISI:000456484300001, title = {Neutral-Atom Wavelength-Compatible 780 nm Single Photons from a Trapped Ion via Quantum Frequency Conversion}, journal = {Phys. Rev. Appl.}, volume = {11}, number = {1}, year = {2019}, month = {JAN 23}, pages = {014044}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {The interfacing of quantum platforms via photonic links is a precursor for establishing scalable quantum networks. The connection of different types of quantum memories for hybrid networking requires the overcoming of the disparate photon wavelengths emitted by each quantum memory. Given achievements in quantum information processing with trapped-ion and neutral-atom architectures, a hybrid system with modular interconnectivity is advantageous. Here, we use a trapped Ba-138(+) ion and a periodically poled lithium-niobate (PPLN) waveguide, with a fiber-coupled output, to demonstrate 19\% end-to-end efficient quantum frequency conversion (QFC) of single photons from 493 to 780 nm and use fluorescence of the ion to produce light at the Rb-87 D-2 transition wavelength. To demonstrate the quantum nature of both the unconverted 493 nm photons and the converted photons near 780 nm, we observe strong quantum statics in their respective second-order intensity correlations. This work extends the range of intralaboratory networking between ions and networking between disparate quantum memories.}, issn = {2331-7019}, doi = {10.1103/PhysRevApplied.11.014044}, author = {Siverns, James D. and Hannegan, John and Quraishi, Qudsia} } @article { ISI:000496930000002, title = {Quantum Interference between Photons from an Atomic Ensemble and a Remote Atomic Ion}, journal = {Phys. Rev. Lett.}, volume = {123}, number = {21}, year = {2019}, month = {NOV 18}, pages = {213601}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {Many remote-entanglement protocols rely on the generation and interference of photons produced by nodes within a quantum network. Quantum networks based on heterogeneous nodes provide a versatile platform by utilizing the complementary strengths of the differing systems. Implementation of such networks is challenging, due to the disparate spectral and temporal characteristics of the photons generated by the different quantum systems. Here, we report on the observation of quantum interference between photons generated from a single ion and an atomic ensemble. The photons are produced on demand by each source located in separate buildings, in a manner suitable for quantum networking. Given these results, we analyze the feasibility of hybrid ion-ensemble remote entanglement generation.}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.123.213601}, author = {Craddock, A. N. and Hannegan, J. and Ornelas-Huerta, D. P. and Siverns, J. D. and Hachtel, A. J. and Goldschmidt, A. and Porto, J. V. and Quraishi, Q. and Rolston, S. L.} } @article { ISI:000438672400001, title = {Energy-level statistics in strongly disordered systems with power-law hopping}, journal = {PHYSICAL REVIEW B}, volume = {98}, number = {1}, year = {2018}, month = {JUL 16}, pages = {014201}, issn = {2469-9950}, doi = {10.1103/PhysRevB.98.014201}, author = {Titum, Paraj and Quito, Victor L. and Syzranov, V, Sergey} } @article {ISI:000353916300007, title = {Tunable Spin-Orbit Coupling via Strong Driving in Ultracold-Atom Systems}, journal = {PHYSICAL REVIEW LETTERS}, volume = {114}, number = {12}, year = {2015}, month = {MAR 24}, pages = {125301}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.114.125301}, author = {Jimenez-Garcia, K. and LeBlanc, L. J. and Williams, R. A. and Beeler, M. C. and Qu, C. and Gong, M. and Zhang, C. and Ian B Spielman} } @article { ISI:000337107100040, title = {Beat note stabilization of mode-locked lasers for quantum information processing}, journal = {OPTICS LETTERS}, volume = {39}, number = {11}, year = {2014}, month = {JUN 1}, pages = {3238-3241}, issn = {0146-9592}, doi = {10.1364/OL.39.003238}, author = {Islam, R. and Campbell, W. C. and Choi, T. and Clark, S. M. and Conover, C. W. S. and Debnath, S. and Edwards, E. E. and Fields, B. and Hayes, D. and Hucul, D. and Inlek, I. V. and Johnson, K. G. and Korenblit, S. and Lee, A. and Lee, K. W. and Manning, T. A. and Matsukevich, D. N. and Mizrahi, J. and Quraishi, Q. and C. Senko and Smith, J. and C. Monroe} } @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} } @article {2537, title = {Coherent Error Suppression in Multiqubit Entangling Gates}, journal = {PHYSICAL REVIEW LETTERS}, volume = {109}, year = {2012}, month = {JUL 11}, pages = {020503}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.109.020503}, author = {Hayes, D. and Clark, S. M. and Debnath, S. and Hucul, D. and Inlek, I. V. and Lee, K. W. and Quraishi, Q. and C. Monroe} } @article { ISI:000308575500007, title = {Ultracold Molecules under Control!}, journal = {CHEMICAL REVIEWS}, volume = {112}, number = {9, SI}, year = {2012}, month = {SEP}, pages = {4949-5011}, issn = {0009-2665}, doi = {10.1021/cr300092g}, author = {Quemener, Goulven and Julienne, Paul S.} } @article {Hayes2010, title = {Entanglement of Atomic Qubits Using an Optical Frequency Comb}, journal = {Phys. Rev. Lett.}, volume = {104}, number = {14}, year = {2010}, month = {apr}, pages = {140501}, keywords = {Single Fellow}, issn = {0031-9007}, url = {http://prl.aps.org/abstract/PRL/v104/i14/e140501}, author = {David Hayes and D N Matsukevich and P Maunz and D Hucul and Q Quraishi and Steven Olmschenk and W C Campbell and J Mizrahi and Crystal Senko and Christopher Monroe} } @article {Ropp2010a, title = {Positioning and immobilization of individual quantum dots with nanoscale precision}, journal = {Nano Lett.}, volume = {10}, number = {11}, year = {2010}, month = {nov}, pages = {4673{\textendash}9}, publisher = {American Chemical Society}, abstract = {We demonstrate a technique for the precise immobilization of nanoscale objects at accurate positions on two-dimensional surfaces. We have developed a water-based photoresist that causes nanostructures such as colloidal quantum dots to segregate to a thin layer at surfaces. By combining this material with electroosmotic feedback control, we demonstrate the ability to position selected, individual quantum dots at specific locations and to immobilize them with 130 nm precision via localized UV exposure.

}, keywords = {2010, Adhesiveness, Electroplating, Electroplating: methods, Materials Testing, Micromanipulation, Micromanipulation: methods, Quantum Dots, Single Fellow, Surface Properties, Ultraviolet Rays}, issn = {1530-6992}, url = {http://dx.doi.org/10.1021/nl1029557}, author = {Ropp, Chad and Cummins, Zachary and Probst, Roland and Qin, Sijia and John T Fourkas and Shapiro, Benjamin and Edo Waks} } @article {2460, title = {The quantum spin Hall effect and topological insulators}, journal = {Physics Today}, volume = {63}, year = {2010}, month = {1/2010}, doi = {10.1063/1.3293411}, author = {Xiao-Liang Qi and Shou-Cheng Zhang} } @article {Ospelkaus2010, title = {Quantum-state controlled chemical reactions of ultracold potassium-rubidium molecules}, journal = {Science}, volume = {327}, number = {5967}, year = {2010}, month = {feb}, pages = {853{\textendash}7}, abstract = {How does a chemical reaction proceed at ultralow temperatures? Can simple quantum mechanical rules such as quantum statistics, single partial-wave scattering, and quantum threshold laws provide a clear understanding of the molecular reactivity under a vanishing collision energy? Starting with an optically trapped near-quantum-degenerate gas of polar 40K87Rb molecules prepared in their absolute ground state, we report experimental evidence for exothermic atom-exchange chemical reactions. When these fermionic molecules were prepared in a single quantum state at a temperature of a few hundred nanokelvin, we observed p-wave-dominated quantum threshold collisions arising from tunneling through an angular momentum barrier followed by a short-range chemical reaction with a probability near unity. When these molecules were prepared in two different internal states or when molecules and atoms were brought together, the reaction rates were enhanced by a factor of 10 to 100 as a result of s-wave scattering, which does not have a centrifugal barrier. The measured rates agree with predicted universal loss rates related to the two-body van der Waals length.}, keywords = {2010}, issn = {1095-9203}, url = {http://www.sciencemag.org/content/327/5967/853.abstract}, author = {Ospelkaus, S. and Ni, K.-K. and Wang, D. and de Miranda, M. H. G. and B Neyenhuis and Qu{\'e}m{\'e}ner, G and Paul S Julienne and Bohn, J L and D S Jin and Jun Ye} } @article {Campbell2010, title = {Ultrafast Gates for Single Atomic Qubits}, journal = {Phys. Rev. Lett.}, volume = {105}, number = {9}, year = {2010}, month = {aug}, pages = {090502}, abstract = {We demonstrate the use of an optical frequency comb to coherently control and entangle atomic qubits. A train of off-resonant ultrafast laser pulses is used to efficiently and coherently transfer population between electronic and vibrational states of trapped atomic ions and implement an entangling quantum logic gate with high fidelity. This technique can be extended to the high field regime where operations can be performed faster than the trap frequency. This general approach can be applied to more complex quantum systems, such as large collections of interacting atoms or molecules.

}, keywords = {2010, Single Fellow}, issn = {0031-9007}, url = {http://prl.aps.org/abstract/PRL/v105/i9/e090502}, author = {W C Campbell and J Mizrahi and Q Quraishi and Crystal Senko and David Hayes and D Hucul and D N Matsukevich and P Maunz and Christopher Monroe and Steven Olmschenk} }