Bulletin of the American Physical Society
2013 Joint Meeting of the APS Division of Atomic, Molecular & Optical Physics and the CAP Division of Atomic, Molecular & Optical Physics, Canada
Volume 58, Number 6
Monday–Friday, June 3–7, 2013; Quebec City, Canada
Session N5: Quantum Simulations and Dynamics |
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Chair: James Freericks, Georgetown University Room: 301 |
Thursday, June 6, 2013 10:30AM - 10:42AM |
N5.00001: Quantum simulation by filtered Hamiltonian engineering Ashok Ajoy, Paola Cappellaro We present a method for Hamiltonian engineering in quantum information processing architectures that requires no local control, but only relies on collective qubit rotations and static field gradients. The technique achieves a spatial modulation of the coupling strengths via a dynamical construction of a weighting function combined with a Bragg grating. As an example, we demonstrate how to generate the ideal Hamiltonian for perfect quantum information transport between two separated nodes of a large spin network. ~We engineer a spin chain with optimal couplings from a large spin network, such as naturally occurring in crystals, while decoupling all unwanted interactions. For realistic experimental parameters, our method can be used to drive perfect quantum information transport at room-temperature. The Hamiltonian engineering method can be applied to a variety of physical systems, for example trapped ions, or Rydberg atoms in optical lattices. It can be made more robust under decoherence and coupling disorder by a novel apodization scheme. Thus the method is quite general and can be used engineer the Hamiltonian of many complex spin lattices with different 2D or 3D coupling topologies. [Preview Abstract] |
Thursday, June 6, 2013 10:42AM - 10:54AM |
N5.00002: Adiabatic Quantum Computation with Neutral Cesium Aaron Hankin, L. Paul Parazzoli, Chin-Wen Chou, Yuan-Yu Jau, George Burns, Amber Young, Shanalyn Kemme, Andrew Ferdinand, Grant Biedermann, Andrew Landahl We are implementing a new platform for adiabatic quantum computation (AQC) [1] based on trapped neutral atoms whose coupling is mediated by the dipole-dipole interactions of Rydberg states. Ground state cesium atoms are dressed by laser fields in a manner conditional on the Rydberg blockade mechanism [2,3], thereby providing the requisite entangling interactions. As a benchmark we study a Quadratic Unconstrained Binary Optimization (QUBO) problem whose solution is found in the ground state spin configuration of an Ising-like model.\\[4pt] [1] E. Farhi, et al. Science 292, 472 (2000)\\[0pt] [2] S. Rolston, et al. Phys. Rev. A, 82, 033412 (2010)\\[0pt] [3] T. Keating, et al. arXiv:1209.4112 (2012) [Preview Abstract] |
Thursday, June 6, 2013 10:54AM - 11:06AM |
N5.00003: On Heat in a Quantum Mechanical Process Tanapat Deesuwan, Janet Anders Heat is the portion of energy exchange between systems in thermodynamic process which, unlike work, is always associated with the change of the entropies of the systems. In the context of quantum thermodynamics, heat process is described by an incoherent generalised quantum evolution, which is a map between two quantum states that does not preserve the entropy. Based on an information-theoretic reasoning, we propose that heat involving in a general quantum thermodynamic process can be separated into two types: one that is due to the unital subclass of the evolutions and another one that is due to the others. According to these categories, we show how the former type of heat can be incorporated into Jarzynski equality, resulting in a generalised version of the equality. We also derive a Jarzynski inequality which incorporates all heat into the picture and show that this situation is just equivalent to the presence of Maxwell's demon. [Preview Abstract] |
Thursday, June 6, 2013 11:06AM - 11:18AM |
N5.00004: Optimizing Adiabaticity in a Trapped-Ion Quantum Simulator Phil Richerme, Crystal Senko, Simcha Korenblit, Jacob Smith, Aaron Lee, Christopher Monroe Trapped-ion quantum simulators are a leading platform for the study of interacting spin systems, such as fully-connected Ising models with transverse and axial fields. Phonon-mediated spin-dependent optical dipole forces act globally on a linear chain of trapped Yb-171+ ions to generate the spin-spin couplings, with the form and range of such couplings controlled by laser frequencies and trap voltages. The spins are initially prepared along an effective transverse magnetic field, which is large compared to the Ising couplings and slowly ramped down during the quantum simulation. The system remains in the ground state throughout the evolution if the ramp is adiabatic, and the spin ordering is directly measured by state-dependent fluorescence imaging of the ions onto a camera. Two techniques can improve the identification of the ground state at the end of simulations that are unavoidably diabatic. First, we show an optimized ramp protocol that gives a maximal probability of measuring the true ground state given a finite ramp time. Second, we show that no spin ordering is more prevalent than the ground state(s), even for non-adiabatic ramps. [Preview Abstract] |
Thursday, June 6, 2013 11:18AM - 11:30AM |
N5.00005: Quantum simulation of open-system dynamical maps with trapped ions P. Schindler, M. Mueller, D. Nigg, J.T. Barreiro, E.A. Martinez, M. Hennrich, T. Monz, S. Diehl, P. Zoller, R. Blatt Dynamical maps describe general transformations of the state of a physical system, and their iteration can be interpreted as generating a discrete time evolution. Quantum mechanical examples show intriguing phenomena such as dynamical localization on the single-particle level. We extend the concept of dynamical maps to an open-system, many-particle context: We experimentally explore the stroboscopic dynamics of a complex many-body spin model by means of a universal quantum simulator using up to five ions. In particular, we generate long-range phase coherence of spin by an iteration of purely dissipative quantum maps. We also demonstrate the characteristics of competition between combined coherent and dissipative non-equilibrium evolution. This opens the door for studying many-particle non-equilibrium physics and associated dynamical phase transitions with no immediate counterpart in equilibrium condensed matter systems. As a first step in this direction, we developed an error detection and reduction toolbox that facilitates the faithful quantum simulation of larger systems. [Preview Abstract] |
Thursday, June 6, 2013 11:30AM - 11:42AM |
N5.00006: Dynamical Entanglement Creation and Measurement with Cold Atoms or Ions Johannes Schachenmayer, Hannes Pichler, Peter Zoller, Ben Lanyon, Andrew Daley Systems of cold atoms in optical lattices or a string of ions in a linear trap offer a controlled environment to experimentally study non-equilibrium dynamics of 1D many-body quantum systems with interactions of varying range. In these systems, the question of how the entanglement entropy between different blocks of a many-body state evolves as a function of time is an important one, since it determines whether the evolution of the system can be efficiently simulated on a classical computer. States with large-scale entanglement offer regimes where quantum simulators could be used to outperform classical simulation, and thus there is a great interest to produce large-scale entanglement in these types of experiments. Here we present analytical and numerical results on the entanglement entropy growth behavior in 1D lattice systems after a sudden change of a model parameter, and the dependence of this growth on the range of the interactions. Furthermore we show, how entanglement entropies can be directly measured in realistic experiments. [Preview Abstract] |
Thursday, June 6, 2013 11:42AM - 11:54AM |
N5.00007: Behaviour of quantum correlations in a non-equilibrium system at criticality Chaitanya Joshi, Jonathan Keeling Even though coupling an interacting quantum system to a reservoir leads to dissipation and decoherence, there can nevertheless be non-trivial phase diagrams and critical properties of open quantum systems. As for a closed system, the exponentially large Hilbert space can however be a problem in studying such systems. Decoherence may however be expected to reduce the required size of the Hilbert space. Matrix product states (MPS) are one representation to allow tractable numerics on a strongly correlated multipartite quantum system. Although MPS have proved to be an accurate description for a closed system, we explore how the MPS state description fares in a dissipative driven system close to criticality. We pose the question how does quantum correlation length behave at the phase transition and if it does not diverge at the critical point in a dissipative system then is a finite rank MPS representation still a good approximation of the respective state. [Preview Abstract] |
Thursday, June 6, 2013 11:54AM - 12:06PM |
N5.00008: Nucleation and Dynamics of Topological Defects in Trapped Yb Ion-crystals Sara Ejtemaee, Paul C. Haljan Topological defects, formed as a result of symmetry breaking in continuous phase transitions, have been observed in a range of physical systems. Included among these systems, laser cooled arrays of trapped ions, also known as ion crystals, are well suited to the study of nucleation and dynamics of defects since they are a highly controllable system in which defects can be imaged directly. In ion crystals, a rapid quench across the structural phase transition from linear to a two-dimensional zigzag configuration can lead to the formation of topological defects, which appear as ``kinks'' in the crystal structure. In this presentation, we report on defects created in a crystal of trapped $^{174}Yb$ ions, which is brought through the linear-to-zigzag phase transition by relaxing the transverse confinement. We measure the number of defects formed as a function of quench rate, and compare our results to simulations and theoretically predicted rates of nucleation. We also study the dynamics of the defects, including their lifetime in the ion crystal, their motion, and the occurrence of two different forms of defect, discrete and extended. [Preview Abstract] |
Thursday, June 6, 2013 12:06PM - 12:18PM |
N5.00009: The role of resonant and off-resonant modes in Non-Markovian behaviour Vignesh Venkataraman, Douglas Plato, Myungshik Kim For some solid state and biological systems, a master equation approach using a Markov approximation will not accurately describe the dynamical behaviour and therefore work has been done to quantify the amount of non-Markovian behaviour in a model. We investigate a harmonic oscillator coupled to a bath of oscillators under the rotating wave approximation using a covariance matrix approach. Concentrating on an entanglement based non- Markovianity measure proposed by Rivas et al [1] we consider the role resonant and off-resonant modes play in affecting the measure. We use a large finite bath of oscillators for both Ohmic and Super Ohmic spectral densities and find, by varying the coupling strength, that at small values the resonant modes have the greatest effect but after a certain threshold of coupling strength the off-resonant modes play the dominant role. \\[4pt] [1] A. Rivas, S. F. Huelga, and M. B. Plenio, Phys. Rev. Lett. 105, 050403 (2010) [Preview Abstract] |
Thursday, June 6, 2013 12:18PM - 12:30PM |
N5.00010: Robust Online Hamiltonian Learning Christopher Granade, Christopher Ferrie, Nathan Wiebe, David Cory In this talk, we introduce a machine-learning algorithm for the problem of inferring the dynamical parameters of a quantum system, and discuss this algorithm in the example of estimating the precession frequency of a single qubit in a static field. Our algorithm is designed with practicality in mind by including parameters that control trade-offs between the requirements on computational and experimental resources. The algorithm can be implemented online, during experimental data collection, or can be used as a tool for post-processing. Most importantly, our algorithm is capable of learning Hamiltonian parameters even when the parameters change from experiment-to-experiment, and also when additional noise processes are present and unknown. Finally, we discuss the performance of the our algorithm by appeal to the Cramer-Rao bound. [Preview Abstract] |
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