Person: Gorshkov, Alexey
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Gorshkov
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Alexey
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Gorshkov, Alexey
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Publication Quantum Nonlinear Optics with Single Photons Enabled by Strongly Interacting Atoms(Nature Publishing Group, 2012) Peyronel, Thibault; Firstenberg, Ofer; Liang, Qi-Yu; Hofferberth, Sebastian; Gorshkov, Alexey; Pohl, Thomas; Lukin, Mikhail; Vuletić, VladanThe realization of strong nonlinear interactions between individual light quanta (photons) is a long-standing goal in optical science and engineering, being of both fundamental and technological significance. In conventional optical materials, the nonlinearity at light powers corresponding to single photons is negligibly weak. Here we demonstrate a medium that is nonlinear at the level of individual quanta, exhibiting strong absorption of photon pairs while remaining transparent to single photons. The quantum nonlinearity is obtained by coherently coupling slowly propagating photons to strongly interacting atomic Rydberg states in a cold, dense atomic gas. Our approach paves the way for quantum-by-quantum control of light fields, including single-photon switching, all-optical deterministic quantum logic and the realization of strongly correlated many-body states of light.Publication Attractive photons in a quantum nonlinear medium(Springer Nature, 2013) Firstenberg, Ofer; Peyronel, Thibault; Liang, Qi-Yu; Gorshkov, Alexey; Lukin, Mikhail; Vuletić, VladanThe fundamental properties of light derive from its constituent particles—massless quanta (photons) that do not interact with one another\(^1\). However, it has long been known that the realization of coherent interactions between individual photons, akin to those associated with conventional massive particles, could enable a wide variety of novel scientific and engineering applications\(^{2,3}\). Here we demonstrate a quantum nonlinear medium inside which individual photons travel as massive particles with strong mutual attraction, such that the propagation of photon pairs is dominated by a two-photon bound state\(^{4–7}\). We achieve this through dispersive coupling of light to strongly interacting atoms in highly excited Rydberg states. We measure the dynamical evolution of the two-photon wavefunction using time-resolved quantum state tomography, and demonstrate a conditional phase shift8 exceeding one radian, resulting in polarization-entangled photon pairs. Particular applications of this technique include all-optical switching, deterministic photonic quantum logic and the generation of strongly correlated states of light\(^9\).Publication Far-Field Optical Imaging and Manipulation of Individual Spins with Nanoscale Resolution(Nature Publishing Group, 2010) Maurer, Peter Christian; Maze, J. R.; Stanwix, P. L.; Jiang, L.; Gorshkov, Alexey; Zibrov, A. A.; Harke, B.; Hodges, J. S.; Zibrov, Alexander; Yacoby, Amir; Twitchen, D.; Hell, S. W.; Walsworth, Ronald; Lukin, MikhailA fundamental limit to existing optical techniques for measurementand manipulation of spin degrees of freedom is set by diffraction, which does not allow spins separated by less than about a quarter of a micrometre to be resolved using conventional far-field optics. Here, we report an efficient far-field optical technique that overcomes the limiting role of diffraction, allowing individual electronic spins to be detected, imaged and manipulated coherently with nanoscale resolution. The technique involves selective flipping of the orientation of individual spins, associated with nitrogen-vacancy centres in room-temperature diamond, using a focused beam of light with intensity vanishing at a controllable location, which enables simultaneous single-spin imaging and magnetometry at the nanoscale with considerably less power than conventional techniques. Furthermore, by inhibiting spin transitions away from the laser intensity null, selective coherent rotation of individual spins is realized. This technique can be extended to subnanometre dimensions, thus enabling applications in diverse areas ranging from quantum information science to bioimaging.Publication Two-orbital SU(N) magnetism with ultracold alkaline-earth atoms(Nature Publishing Group, 2010) Gorshkov, Alexey; Hermele, M.; Gurarie, V.; Xu, C; Julienne, P. S.; Ye, J.; Zoller, P.; Demler, Eugene; Lukin, Mikhail; Rey, A. M.Fermionic alkaline-earth atoms have unique properties that make them attractive candidates for the realization of atomic clocks and degenerate quantum gases. At the same time, they are attracting considerable theoretical attention in the context of quantum information processing. Here we demonstrate that when such atoms are loaded in optical lattices, they can be used as quantum simulators of unique many-body phenomena. In particular, we show that the decoupling of the nuclear spin from the electronic angular momentum can be used to implement many-body systems with an unprecedented degree of symmetry, characterized by the SU(N) group with N as large as 10. Moreover, the interplay of the nuclear spin with the electronic degree of freedom provided by a stable optically excited state should enable the study of physics governed by the spin–orbital interaction. Such systems may provide valuable insights into the physics of strongly correlated transition-metal oxides, heavy-fermion materials and spin-liquid phases.Publication Scattering resonances and bound states for strongly interacting Rydberg polaritons(American Physical Society (APS), 2014) Bienias, P.; Choi, S.; Firstenberg, O.; Maghrebi, M. F.; Gullans, M.; Lukin, Mikhail; Gorshkov, Alexey; Büchler, H. P.We provide a theoretical framework describing slow-light polaritons interacting via atomic Rydberg states. The method allows us to analytically derive the scattering properties of two polaritons. We identify parameter regimes where polariton-polariton interactions are repulsive. Furthermore, in the regime of attractive interactions, we identify multiple two-polariton bound states, calculate their dispersion, and study the resulting scattering resonances. Finally, the two-particle scattering properties allow us to derive the effective low-energy many-body Hamiltonian. This theoretical platform is applicable to ongoing experiments.Publication Scalable Architecture for a Room Temperature Solid-State Quantum Information Processor(Nature Publishing Group, 2012) Yao, Norman; Jiang, Liang; Gorshkov, Alexey; Maurer, Peter Christian; Giedke, Géza; Cirac, Ignacio; Lukin, MikhailThe realization of a scalable quantum information processor has emerged over the past decade as one of the central challenges at the interface of fundamental science and engineering. Here we propose and analyse an architecture for a scalable, solid-state quantum information processor capable of operating at room temperature. Our approach is based on recent experimental advances involving nitrogen-vacancy colour centres in diamond. In particular, we demonstrate that the multiple challenges associated with operation at ambient temperature, individual addressing at the nanoscale, strong qubit coupling, robustness against disorder and low decoherence rates can be simultaneously achieved under realistic, experimentally relevant conditions. The architecture uses a novel approach to quantum information transfer and includes a hierarchy of control at successive length scales. Moreover, it alleviates the stringent constraints currently limiting the realization of scalable quantum processors and will provide fundamental insights into the physics of non-equilibrium many-body quantum systems.Publication Robust Quantum State Transfer in Random Unpolarized Spin Chains(American Physical Society, 2011) Yao, Norman; Jiang, Liang; Gorshkov, Alexey; Gong, Zhe-Xuan; Zhai, Alex; Duan, Luming; Lukin, MikhailWe propose and analyze a new approach for quantum state transfer between remote spin qubits. Specifically, we demonstrate that coherent quantum coupling between remote qubits can be achieved via certain classes of random, unpolarized (infinite temperature) spin chains. Our method is robust to coupling-strength disorder and does not require manipulation or control over individual spins. In principle, it can be used to attain perfect state transfer over an arbitrarily long range via purely Hamiltonian evolution and may be particularly applicable in a solid-state quantum information processor. As an example, we demonstrate that it can be used to attain strong coherent coupling between nitrogen-vacancy centers separated by micrometer distances at room temperature. Realistic imperfections and decoherence effects are analyzed.Publication Quantum Magnetism with Polar Alkali-Metal Dimers(American Physical Society, 2011) Gorshkov, Alexey; Manmana, Salvatore; Chen, Gang; Demler, Eugene; Lukin, Mikhail; Rey, AnaWe show that dipolar interactions between ultracold polar alkali dimers in optical lattices can be used to realize a highly tunable generalization of the \(t-J\) model, which we refer to as the \(t-J-V-W\) model. The model features long-range spin-spin interactions \(J_z\) and \(J_{\perp}\) of \(XXZ\) type, long-range density-density interaction \(V\), and long-range density-spin interaction W, all of which can be controlled in both magnitude and sign independently of each other and of the tunneling \(t\). The "spin" is encoded in the rotational degree of freedom of the molecules, while the interactions are controlled by applied static electric and continuous-wave microwave fields. Furthermore, we show that nuclear spins of the molecules can be used to implement an additional (orbital) degree of freedom that is coupled to the original rotational degree of freedom in a tunable way. The presented system is expected to exhibit exotic physics and to provide insights into strongly correlated phenomena in condensed matter systems. Realistic experimental imperfections are discussed.Publication Fast Entanglement Distribution with Atomic Ensembles and Fluorescent Detection(American Physical Society, 2010) Brask, Jonatan; Jiang, Liang; Gorshkov, Alexey; Vuletic, Vladan; Sorensen, Anders; Lukin, MikhailQuantum repeaters based on atomic ensemble quantum memories are promising candidates for achieving scalable distribution of entanglement over long distances. Recently, important experimental progress has been made toward their implementation. However, the entanglement rates and scalability of current approaches are limited by relatively low retrieval and single-photon detector efficiencies. We propose a scheme which makes use of fluorescent detection of stored excitations to significantly increase the efficiency of connection and hence the rate. Practical performance and possible experimental realizations of the new protocol are discussed.Publication Coherent Quantum Optical Control with Subwavelength Resolution(American Physical Society, 2008) Gorshkov, Alexey; Jiang, Liang; Greiner, Markus; Zoller, Peter; Lukin, MikhailWe suggest a new method for quantum optical control with nanoscale resolution. Our method allows for coherent far-field manipulation of individual quantum systems with spatial selectivity that is not limited by the wavelength of radiation and can, in principle, approach a few nanometers. The selectivity is enabled by the nonlinear atomic response, under the conditions of electromagnetically induced transparency, to a control beam with intensity vanishing at a certain location. Practical performance of this technique and its potential applications to quantum information science with cold atoms, ions, and solid-state qubits are discussed.