@article {3056, title = {Advantages and limitations of quantum routing}, journal = {PRX Quantum}, volume = {4}, year = {2023}, month = {2/1/2023}, abstract = {

The Swap gate is a ubiquitous tool for moving information on quantum hardware, yet it can be considered a classical operation because it does not entangle product states. Genuinely quantum operations could outperform Swap for the task of permuting qubits within an architecture, which we call routing. We consider quantum routing in two models: (1) allowing arbitrary two-qubit unitaries, or (2) allowing Hamiltonians with norm-bounded interactions. We lower bound the circuit depth or time of quantum routing in terms of spectral properties of graphs representing the architecture interaction constraints, and give a generalized upper bound for all simple connected n-vertex graphs. In particular, we give conditions for a superpolynomial classical-quantum routing separation, which exclude graphs with a small spectral gap and graphs of bounded degree. Finally, we provide examples of a quadratic separation between gate-based and Hamiltonian routing models with a constant number of local ancillas per qubit and of an Ω(n) speedup if we also allow fast local interactions.

}, keywords = {Data Structures and Algorithms (cs.DS), FOS: Computer and information sciences, FOS: Physical sciences, Quantum Physics (quant-ph)}, doi = {https://doi.org/10.1103/PRXQuantum.4.010313}, url = {https://arxiv.org/abs/2206.01766}, author = {Bapat, Aniruddha and Andrew M. Childs and Alexey V. Gorshkov and Schoute, Eddie} } @article {2594, title = {Asymmetric blockade and multi-qubit gates via dipole-dipole interactions}, year = {2020}, month = {6/3/2020}, abstract = {

Due to their strong and tunable interactions, Rydberg atoms can be used to realize fast two-qubit entangling gates. We propose a generalization of a generic two-qubit Rydberg-blockade gate to multi-qubit Rydberg-blockade gates which involve both many control qubits and many target qubits simultaneously. This is achieved by using strong microwave fields to dress nearby Rydberg states, leading to asymmetric blockade in which control-target interactions are much stronger than control-control and target-target interactions. The implementation of these multi-qubit gates can drastically simplify both quantum algorithms and state preparation. To illustrate this, we show that a 25-atom GHZ state can be created using only three gates with an error of 7.8\%.

}, url = {https://arxiv.org/abs/2006.02486}, author = {Jeremy T. Young and Przemyslaw Bienias and Ron Belyansky and Adam M. Kaufman and Alexey V. Gorshkov} } @article {2211, title = {Asymmetric Particle Transport and Light-Cone Dynamics Induced by Anyonic Statistics}, journal = {Phys. Rev. Lett}, volume = {121}, year = {2018}, month = {2018/12/20}, abstract = {

We study the non-equilibrium dynamics of Abelian anyons in a one-dimensional system. We find that the interplay of anyonic statistics and interactions gives rise to spatially asymmetric particle transport together with a novel dynamical symmetry that depends on the anyonic statistical angle and the sign of interactions. Moreover, we show that anyonic statistics induces asymmetric spreading of quantum information, characterized by asymmetric light cones of out-of-time-ordered correlators. Such asymmetric dynamics is in sharp contrast with the dynamics of conventional fermions or bosons, where both the transport and information dynamics are spatially symmetric. We further discuss experiments with cold atoms where the predicted phenomena can be observed using state-of-the-art technologies. Our results pave the way toward experimentally probing anyonic statistics through non-equilibrium dynamics.

}, doi = {https://doi.org/10.1103/PhysRevLett.121.250404}, url = {https://arxiv.org/abs/1809.02614}, author = {Fangli Liu and James R. Garrison and Dong-Ling Deng and Zhe-Xuan Gong and Alexey V. Gorshkov} } @article {1678, title = {Anomalous broadening in driven dissipative Rydberg systems}, journal = {Physical Review Letters}, volume = {116}, year = {2016}, month = {2016/03/16}, pages = {113001}, abstract = {We observe interaction-induced broadening of the two-photon 5s-18s transition in 87Rb atoms trapped in a 3D optical lattice. The measured linewidth increases by nearly two orders of magnitude with increasing atomic density and excitation strength, with corresponding suppression of resonant scattering and enhancement of off-resonant scattering. We attribute the increased linewidth to resonant dipole-dipole interactions of 18s atoms with spontaneously created populations of nearby np states. Over a range of initial atomic densities and excitation strengths, the transition width is described by a single function of the steady-state density of Rydberg atoms, and the observed resonant excitation rate corresponds to that of a two-level system with the measured, rather than natural, linewidth. The broadening mechanism observed here is likely to have negative implications for many proposals with coherently interacting Rydberg atoms.}, doi = {10.1103/PhysRevLett.116.113001}, url = {http://arxiv.org/abs/1510.08710}, author = {E. A. Goldschmidt and T. Boulier and R. C. Brown and S. B. Koller and J. T. Young and Alexey V. Gorshkov and S. L. Rolston and J. V. Porto} } @article {1838, title = {Atom induced cavities and tunable long-range interactions between atoms trapped near photonic crystals}, journal = {Nature Photon. 9, 326 (2015)}, year = {2015}, month = {2015/03/03}, abstract = {

Using cold atoms to simulate strongly interacting quantum systems represents an exciting frontier of physics. However, achieving tunable, coherent long-range interactions between atoms is an outstanding challenge, which currently leaves a large class of models inaccessible to quantum simulation. Here, we propose a solution exploiting the powerful new platform of cold atoms trapped near nano-photonic systems. We show that the dielectric contrast of an atom trapped near a photonic crystal can seed a localized cavity mode around the atomic position. In a dynamic form of \“all-atomic\” cavity QED, the length of these cavity modes can be tuned, and atoms separated by the order of the e\↵ective cavity length can interact coherently with each other. Considering realistic conditions such as fabrication disorder and photon losses, coherent long-range potentials or spin interactions can be dominant in the system over length scales up to hundreds of wavelengths.

}, doi = {doi:10.1038/nphoton.2015.57}, url = {http://www.nature.com/nphoton/journal/v9/n5/full/nphoton.2015.57.html}, author = {J S Douglas and H Habibian and Alexey V. Gorshkov and H J Kimble and D E Chang} } @article {1841, title = {Attractive Photons in a Quantum Nonlinear Medium}, journal = {Nature (London)}, volume = {502}, year = {2013}, pages = {71}, url = {http://dx.doi.org/10.1038/nature12512}, author = {Ofer Firstenberg and Thibault Peyronel and Qi-Yu Liang and Alexey V. Gorshkov and Mikhail D. Lukin and Vladan Vuletic} } @article {1193, title = {Alkaline-Earth-Metal Atoms as Few-Qubit Quantum Registers}, journal = {Physical Review Letters}, volume = {102}, year = {2009}, month = {2009/3/18}, abstract = { We propose and analyze a novel approach to quantum information processing, in which multiple qubits can be encoded and manipulated using electronic and nuclear degrees of freedom associated with individual alkaline-earth atoms trapped in an optical lattice. Specifically, we describe how the qubits within each register can be individually manipulated and measured with sub-wavelength optical resolution. We also show how such few-qubit registers can be coupled to each other in optical superlattices via conditional tunneling to form a scalable quantum network. Finally, potential applications to quantum computation and precision measurements are discussed. }, doi = {10.1103/PhysRevLett.102.110503}, url = {http://arxiv.org/abs/0812.3660v2}, author = {Alexey V. Gorshkov and Ana Maria Rey and Andrew J. Daley and Martin M. Boyd and Jun Ye and Peter Zoller and Mikhail D. Lukin} } @article {1192, title = {Anyonic interferometry and protected memories in atomic spin lattices}, journal = {Nature Physics}, volume = {4}, year = {2008}, month = {2008/4/20}, pages = {482 - 488}, abstract = { 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. }, doi = {10.1038/nphys943}, url = {http://arxiv.org/abs/0711.1365v1}, author = {Liang Jiang and Gavin K. Brennen and Alexey V. Gorshkov and Klemens Hammerer and Mohammad Hafezi and Eugene Demler and Mikhail D. Lukin and Peter Zoller} }