All seminars below will take place on Mondays at 12:30 PM in room 1201 of the Physics Building. Lunch will be served in the Physics Toll room at Noon.
- September 14th
Title: Coupling a photon and an atom in free space
Speaker: Gerd Leuchs, University of Erlangen, Germany
Abstract: The interaction of a single photon with a single atom in free space is probably one of the most fundamental processes in quantum optics. If the atom is initially in the excited state and the field in the vacuum state, the system will decay to the atom in the ground state and the photon in a wave packet in the far field. This spontaneous emission process is a unitary evolution. Thus, the process should also be able to run backwards starting with the photon in the far field and the atom unexcited – leading to a fully excited atom every single time the experiment is done. We are currently setting up an experiment to show that the probability for the absorption of the single photon can indeed be one [1]. In the presentation potential complications and counter measures are discussed. If successful, the experimental set-up can be used to do non linear optics at the single photon level and to implement quantum gates for quantum information processing. This free space approach is an alternative to other schemes using an optical resonator or a nano optical plasmonic antenna to reach maximum coupling between an atom and a photon.
[1] R. Maiwald, G. Leuchs, D. Leibfried, J. Britton, J.C. Bergquist, D.J. Wineland
"Stylus ion trap for enhanced access and sensing",
Nature Physics 5, 551 (2009) (arXiv: 0810.2647)
- September 21st
Title: Synthetic vector potentials and electromagnetic fields created with light
Speaker: Ian Spielman, JQI/NIST
Abstract: Ultra cold atoms are remarkable systems with a truly unprecedented level of experimental control and one application of this control is engineering the systems hamiltonian. To date this has focused mostly on the real-space potential that the atoms experience for example, multiple-well traps or optical lattice potentials. Here I present our experimental work which tailors the energy-momentum dispersion of the cold atoms. We couple different internal states of rubidium 87 via a momentum-selective Raman transition and load our system into the resulting adiabatic eigenstates. Using this technique we show the controlled modification of the energy-momentum dispersion leads to a synthetic vector potential.
With the engineered vector potential in hand, we will see how suitable time dependence leads to synthetic electric fields and how spatial gradients can produce synthetic magnetic fields.
- September 28th
Title: Entanglement, quantum criticality, and coherent dynamics in many-atom and many-ion systems
Speaker: Joel Moore, University of California, Berkeley and Lawrence Berkeley National Laboratory
Abstract: Concepts from quantum information theory, such as "entanglement", are giving insight into long-standing problems in the physics of interacting particles, such as the nature of quantum critical states. At the same time, experiments on atomic and ionic systems, stimulated by the goal of quantum computing, are studying the quantum coherent dynamics of many-particle systems with much greater precision than previously possible. We first review the importance of entanglement for the theory of quantum critical ground states, primarily using one-dimensional models as an example: such ground states are infinitely more entangled than ordinary ground states, and a theory is presented for how this entanglement leads to universal errors ("finite-entanglement scaling") in any finite-entanglement representation, such as in a classical computer. We then discuss the zero-temperature coherent dynamics of many-particle states as studied in recent atomic physics experiments. We focus on the question of how thermalization/ equilibration occurs in fully coherent dynamics, using a combination of analytical and numerical methods. Current experiments offer the potential to settle many debates about equilibration and the foundations of statistical physics.
- October 5th
Title: How does a quantum mechanical system thermalize?
Speaker: David Weiss, Pennsylvania State University
Abstract: I will describe experiments with atoms in optical lattices that create effectively 1D Bose gases. These are the first experimentally observed integrable many-body systems, which means among other things that they can be exactly solved and that to a first approximation they do not thermalize, as we have observed by making quantum Newton's cradles. The question we are now addressing is what happens when integrability is lifted. Does the gas thermalize, or, as in some classical systems, is there some regime of non-integrability in which the system still does not thermalize? We think we are close to a definitive experimental answer, but since it's still preliminary. You'll have to come to my talk to hear it.
- October 12th
Title: Demonstration of a Rydberg blockade CNOT gate between two neutral atoms
Speaker: Mark Saffman, University of Wisconsin
Abstract: I will present experimental data demonstrating a two-atom CNOT gate at an atomic separation of 10 microns using Rydberg state mediated interactions. We also show that the CNOT gate can be used to create two-atom entangled states. In addition to quantum gates the long range Rydberg interaction appears well suited for generating many particle entanglement, and deterministic quantum interfaces between matter and photonic qubits. I will discuss some examples of these quantum information applications.
- October 19th
Title: TBA
Speaker: Seth Lloyd, MIT
- October 26th
Title: Secret keys and random numbers from quantum non locality
Speaker: Serge Massar, University of Brussels, Belgium
Abstract: Non local correlations are obtained when local measurements are carried out on entangled quantum particles, leading to a violation of a Bell inequality. We discuss how such non local correlations shared can be used to generate random numbers and secret keys. Using non locality allows a higher degree of security than in the more traditional approaches to quantum cryptography, as it is no longer necessary to trust one's devices, nor even to trust quantum mechanics. We will briefly present the first experimental realization of these proposals, carried out at JQI/Maryland.
- November 2nd
Vacant
- November 9th
Title: Multi-photon interactions with ion-channels: From high-resolution control of neuronal activity to possible mechanisms of quantum coherence assisted ion-transport
Speaker: Alipasha Vazir, Howard Hughes Medical Institute, Janelia Farm
Abstract: Ion-channels are involved in many physiological processes, including maintenance of membrane potential, regulation of electrical excitability, and modulation of hormone and neurotransmitter secretion. In the nervous system their coordinated opening and closing generates action potentials that form the basis for intra-neural communication which are essential for information representation and processing. As a result they have been subject to extensive fundamental studies aiming to understand their structure and function as well as to interfere with their function in order to control neuronal response. The latter has recently proven to be a valuable tool for understanding neuronal connectivity. In these approaches optogenetic techniques are used for on demand opening of light gated ion-channels which allow the interrogation of neuronal response in functional networks.
However, most of the current methods are limited to evoking only neuronal response in large cellular population in an untargeted fashion. In this talk I will present some of our recent results on evoking targeted compartmental specific neuronal response with sub-millisecond temporal resolution by combing optogenetic methods with two-photon absorption from femtosecond optical pulses. The unprecedented spatiotemporal resolution of this method and its ability to enable high throughput pair recordings is expected to allow a new range of studies in neuronal circuitry and mechanisms of neuronal input integration on the single cell level. Further, I will discuss the application of ultrafast correlation spectroscopy methods to studies of conformational dynamics of protein complexes underlying function of the voltage gated ion-channels. In this context I will present estimations and discuss the possibility of a vibrational coherence assisted ion transport process and how the associated protein dynamics could potentially be experimentally revealed.
- November 16th
Title: Experimental quantum error correction
Speaker: Raymond Laflamme, Institute for Quantum Computing and University of Waterloo, Canada
Abstract: The Achilles' heel of quantum information processors is the fragility of quantum states and processes. Without a method to control imperfection and imprecision of quantum devices, the probability that a quantum computation succeed will decrease exponentially in the number of gates it requires. In the last ten years, building on the discovery of quantum error correction, accuracy threshold theorems were proved showing that error can be controlled using a reasonable amount of resources as long as the error rate is smaller than a certain threshold. We thus have a scalable theory describing how to control quantum systems. I will briefly review some of the assumptions of the accuracy threshold theorems and comment on experiments that have been done and should be done to turn quantum error correction into an experimental reality.
- November 23rd
Title: Applied Hyperentanglement
Speaker: Paul Kwiat, University of Illinois
Abstract: In addition to displaying strong nonclassical correlations in polarization, energy, momentum and spatial mode, photons from spontaneous downconversion may be entangled in multiple degrees of freedom simultaneously (“hyperentangled”). Such hyperentangled states reside in a much larger Hilbert space, and enable new capabilities in quantum communication and metrology. For example, hyperentanglement enables one to deterministically identify all four maximally entangled Bell states, leading to improved quantum dense coding. I will discuss this results and it’s extensions, in addition to another application, the remote preparation of entangled polarization/spatial-mode states. Specifically, by making a particular measurement on one photon of a hyperentangled pair (effectively a CNOT gate between polarization and spatial mode), Alice may remotely prepare Bob’s photon in entangled state of these two degrees of freedom. One example is a ‘radial-polarization’ state, in which the polarization of a light beam is everywhere radially directed. Such states have been shown to enable the largest possible longitudinal electric field component in the focal point of a lens, as well as the most efficient mode converter for light-atom coupling in free space. More generally, using these techniques, a wide range of other complex entangled polarization-spatial modes may be remotely prepared.The remotely prepared photons were analyzed in two ways, by quantum state tomography of the entire beam in the spin-orbit basis, and by direct tomography of the polarization state over the transverse spatial mode, using a small scanning pinhole.
- November 30th
Title: Is smell a quantum phenomenon?
Speaker: Luca Turin, MIT
Abstract: Our sense of smell is a extraordinarily good at molecular recognition: we can identify tens of thousands of odorants unerringly over a wide concentration range. The mechanism by which this happens do so is still hotly debated. One view is that molecular shape governs smell, but this notion has turned out to have very little predictive power. Some years ago I revived a discredited theory that posits instead that the nose is a vibrational spectroscope, and proposed a possible underlying mechanism, inelastic electron tunneling. In my talk I will review the history and salient facts of this problem and describe some recent experiments that go some way towards settling the question.
- December 7th
Title: Non-equilibrium Dynamics of Strongly Interacting Bosonic and Fermionic Quantum Gases
Speaker: Immanuel Bloch, Max Planck Institute for Quantum Optics, Ludwig-Maximilians University, Munich
Abstract: Ultracold quantum gases offer novel and intriguing possibilities to probe the dynamical evolution of strongly correlated quantum systems far from equilibrium. We report on recent experiments, in which we have analyzed the transport behaviour of fermionic quantum gases in an optical lattices. We find three distinct transport regimes for non-interacting, weakly- and strongly-interacting quantum gas mixtures for both attractive and repulsive interactions. In a second series of experiments we probe the quantum dynamics of 1D ladder systems far from equilibrium. Here we investigate generalized Landau-Zener transitions between two Luttinger liquids, for which we find striking effects of ground state phase transitions that manifest in the dynamical evolution of the system. Finally, we report on our recent experimental progress towards single atom and single site addressing in a 3D optical lattice using a high numerical aperture optical microscope.
