Dissipation can usually induce detrimental decoherence in a quantum system. However, engineered dissipation can be used to prepare and stabilize coherent quantum many-body states. Here, we show that by engineering dissipators containing photon pair operators, one can stabilize an exotic dark state, which is a condensate of photon pairs with a phase-nematic order. In this system, the usual superfluid order parameter, i.e. single-photon correlation, is absent, while the photon pair correlation exhibits long-range order. Although the dark state is not unique due to multiple parity sectors, we devise an additional type of dissipators to stabilize the dark state in a particular parity sector via a diffusive annihilation process which obeys Glauber dynamics in an Ising model. Furthermore, we propose an implementation of these photon-pair dissipators in circuit-QED architecture.

%8 04/02/2019 %G eng %U https://arxiv.org/abs/1904.00016 %0 Journal Article %J New J. Phys. %D 2019 %T Quantum repeaters based on two species trapped ions %A Siddhartha Santra %A Sreraman Muralidharan %A Martin Lichtman %A Liang Jiang %A Christopher Monroe %A Vladimir S. Malinovsky %XWe examine the viability of quantum repeaters based on two-species trapped ion modules for long distance quantum key distribution. Repeater nodes comprised of ion-trap modules of co-trapped ions of distinct species are considered. The species used for communication qubits has excellent optical properties while the other longer lived species serves as a memory qubit in the modules. Each module interacts with the network only via single photons emitted by the communication ions. Coherent Coulomb interaction between ions is utilized to transfer quantum information between the communication and memory ions and to achieve entanglement swapping between two memory ions. We describe simple modular quantum repeater architectures realizable with the ion-trap modules and numerically study the dependence of the quantum key distribution rate on various experimental parameters, including coupling efficiency, gate infidelity, operation time and length of the elementary links. Our analysis suggests crucial improvements necessary in a physical implementation for co-trapped two-species ions to be a competitive platform in long-distance quantum communication.

%B New J. Phys. %V 21 %8 05/02/2019 %G eng %U https://arxiv.org/abs/1811.10723 %N 073002 %R https://doi.org/10.1088/1367-2630/ab2a45 %0 Journal Article %J Physical Review A %D 2013 %T Quantum Logic between Remote Quantum Registers %A Norman Y. Yao %A Zhe-Xuan Gong %A Chris R. Laumann %A Steven D. Bennett %A L. -M. Duan %A Mikhail D. Lukin %A Liang Jiang %A Alexey V. Gorshkov %X We analyze two approaches to quantum state transfer in solid-state spin systems. First, we consider unpolarized spin-chains and extend previous analysis to various experimentally relevant imperfections, including quenched disorder, dynamical decoherence, and uncompensated long range coupling. In finite-length chains, the interplay between disorder-induced localization and decoherence yields a natural optimal channel fidelity, which we calculate. Long-range dipolar couplings induce a finite intrinsic lifetime for the mediating eigenmode; extensive numerical simulations of dipolar chains of lengths up to L=12 show remarkably high fidelity despite these decay processes. We further consider the extension of the protocol to bosonic systems of coupled oscillators. Second, we introduce a quantum mirror based architecture for universal quantum computing which exploits all of the spins in the system as potential qubits. While this dramatically increases the number of qubits available, the composite operations required to manipulate "dark" spin qubits significantly raise the error threshold for robust operation. Finally, as an example, we demonstrate that eigenmode-mediated state transfer can enable robust long-range logic between spatially separated Nitrogen-Vacancy registers in diamond; numerical simulations confirm that high fidelity gates are achievable even in the presence of moderate disorder. %B Physical Review A %V 87 %8 2013/2/6 %G eng %U http://arxiv.org/abs/1206.0014v1 %N 2 %! Phys. Rev. A %R 10.1103/PhysRevA.87.022306 %0 Journal Article %J Nature Communications %D 2013 %T Topologically Protected Quantum State Transfer in a Chiral Spin Liquid %A Norman Y. Yao %A Chris R. Laumann %A Alexey V. Gorshkov %A Hendrik Weimer %A Liang Jiang %A J. Ignacio Cirac %A Peter Zoller %A Mikhail D. Lukin %X Topology plays a central role in ensuring the robustness of a wide variety of physical phenomena. Notable examples range from the robust current carrying edge states associated with the quantum Hall and the quantum spin Hall effects to proposals involving topologically protected quantum memory and quantum logic operations. Here, we propose and analyze a topologically protected channel for the transfer of quantum states between remote quantum nodes. In our approach, state transfer is mediated by the edge mode of a chiral spin liquid. We demonstrate that the proposed method is intrinsically robust to realistic imperfections associated with disorder and decoherence. Possible experimental implementations and applications to the detection and characterization of spin liquid phases are discussed. %B Nature Communications %V 4 %P 1585 %8 2013/3/12 %G eng %U http://arxiv.org/abs/1110.3788v1 %! Nat Comms %R 10.1038/ncomms2531 %0 Journal Article %J Nature Communications %D 2012 %T Scalable Architecture for a Room Temperature Solid-State Quantum Information Processor %A Norman Y. Yao %A Liang Jiang %A Alexey V. Gorshkov %A Peter C. Maurer %A Geza Giedke %A J. Ignacio Cirac %A Mikhail D. Lukin %X The 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. Much progress has been made towards this goal. Indeed, quantum operations have been demonstrated on several trapped ion qubits, and other solid-state systems are approaching similar levels of control. Extending these techniques to achieve fault-tolerant operations in larger systems with more qubits remains an extremely challenging goal, in part, due to the substantial technical complexity of current implementations. Here, we propose and analyze an architecture for a scalable, solid-state quantum information processor capable of operating at or near room temperature. The architecture is applicable to realistic conditions, which include disorder and relevant decoherence mechanisms, and includes a hierarchy of control at successive length scales. Our approach is based upon recent experimental advances involving Nitrogen-Vacancy color centers in diamond and will provide fundamental insights into the physics of non-equilibrium many-body quantum systems. Additionally, the proposed architecture may greatly alleviate the stringent constraints, currently limiting the realization of scalable quantum processors. %B Nature Communications %V 3 %P 800 %8 2012/4/24 %G eng %U http://arxiv.org/abs/1012.2864v1 %! Nat Comms %R 10.1038/ncomms1788 %0 Journal Article %J Physical Review Letters %D 2011 %T Robust Quantum State Transfer in Random Unpolarized Spin Chains %A Norman Y. Yao %A Liang Jiang %A Alexey V. Gorshkov %A Zhe-Xuan Gong %A Alex Zhai %A L. -M. Duan %A Mikhail D. Lukin %X We 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 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. %B Physical Review Letters %V 106 %8 2011/1/27 %G eng %U http://arxiv.org/abs/1011.2762v2 %N 4 %! Phys. Rev. Lett. %R 10.1103/PhysRevLett.106.040505 %0 Journal Article %J Physical Review A %D 2010 %T Fast Entanglement Distribution with Atomic Ensembles and Fluorescent Detection %A Jonatan B. Brask %A Liang Jiang %A Alexey V. Gorshkov %A Vladan Vuletic %A Anders S. Sorensen %A Mikhail D. Lukin %X Quantum 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 towards 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. %B Physical Review A %V 81 %8 2010/2/12 %G eng %U http://arxiv.org/abs/0907.3839v2 %N 2 %! Phys. Rev. A %R 10.1103/PhysRevA.81.020303 %0 Journal Article %J Nature Physics %D 2008 %T Anyonic interferometry and protected memories in atomic spin lattices %A Liang Jiang %A Gavin K. Brennen %A Alexey V. Gorshkov %A Klemens Hammerer %A Mohammad Hafezi %A Eugene Demler %A Mikhail D. Lukin %A Peter Zoller %X Strongly correlated quantum systems can exhibit exotic behavior called topological order which is characterized by non-local correlations that depend on the system topology. Such systems can exhibit remarkable phenomena such as quasi-particles with anyonic statistics and have been proposed as candidates for naturally fault-tolerant quantum computation. Despite these remarkable properties, anyons have never been observed in nature directly. Here we describe how to unambiguously detect and characterize such states in recently proposed spin lattice realizations using ultra-cold atoms or molecules trapped in an optical lattice. We propose an experimentally feasible technique to access non-local degrees of freedom by performing global operations on trapped spins mediated by an optical cavity mode. We show how to reliably read and write topologically protected quantum memory using an atomic or photonic qubit. Furthermore, our technique can be used to probe statistics and dynamics of anyonic excitations. %B Nature Physics %V 4 %P 482 - 488 %8 2008/4/20 %G eng %U http://arxiv.org/abs/0711.1365v1 %N 6 %! Nat Phys %R 10.1038/nphys943 %0 Journal Article %J Physical Review Letters %D 2008 %T Coherence of an optically illuminated single nuclear spin qubit %A Liang Jiang %A M. V. Gurudev Dutt %A Emre Togan %A Lily Childress %A Paola Cappellaro %A J. M. Taylor %A Mikhail D. Lukin %X We investigate the coherence properties of individual nuclear spin quantum bits in diamond [Dutt et al., Science, 316, 1312 (2007)] when a proximal electronic spin associated with a nitrogen-vacancy (NV) center is being interrogated by optical radiation. The resulting nuclear spin dynamics are governed by time-dependent hyperfine interaction associated with rapid electronic transitions, which can be described by a spin-fluctuator model. We show that due to a process analogous to motional averaging in nuclear magnetic resonance, the nuclear spin coherence can be preserved after a large number of optical excitation cycles. Our theoretical analysis is in good agreement with experimental results. It indicates a novel approach that could potentially isolate the nuclear spin system completely from the electronic environment. %B Physical Review Letters %V 100 %8 2008/2/19 %G eng %U http://arxiv.org/abs/0707.1341v2 %N 7 %! Phys. Rev. Lett. %R 10.1103/PhysRevLett.100.073001 %0 Journal Article %J Physical Review Letters %D 2008 %T Coherent Quantum Optical Control with Subwavelength Resolution %A Alexey V. Gorshkov %A Liang Jiang %A Markus Greiner %A Peter Zoller %A Mikhail D. Lukin %X We 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. %B Physical Review Letters %V 100 %8 2008/3/7 %G eng %U http://arxiv.org/abs/0706.3879v2 %N 9 %! Phys. Rev. Lett. %R 10.1103/PhysRevLett.100.093005