Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B19: Progress in Quantum SimulationInvited

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Sponsoring Units: GQI DAMOP Chair: Ivan Deutsch, University of New Mexico Room: 278279 
Monday, March 13, 2017 11:15AM  11:51AM 
B19.00001: Quantum simulations with noisy quantum computers Invited Speaker: Jay Gambetta Quantum computing is a new computational paradigm that is expected to lie beyond the standard model of computation. This implies a quantum computer can solve problems that can't be solved by a conventional computer with tractable overhead. To fully harness this power we need a universal faulttolerant quantum computer. However the overhead in building such a machine is high and a full solution appears to be many years away. Nevertheless, we believe that we can build machines in the near term that cannot be emulated by a conventional computer. It is then interesting to ask what these can be used for. In this talk we will present our advances in simulating complex quantum systems with noisy quantum computers. We will show experimental implementations of this on some small quantum computers. [Preview Abstract] 
Monday, March 13, 2017 11:51AM  12:27PM 
B19.00002: Quantum simulation of the spinboson model: monitoring the bath Invited Speaker: Nicolas Roch The spinboson model occupies a central position in condensed matter physics. It describes the interaction between a twolevel system and a collection of harmonic oscillators or dissipative bath. It was originally developed as a general, fully quantummechanical, framework to account for the dissipation inherent to any quantum system [1]. This formalism was successfully applied to various physical systems weakly coupled to a bosonic bath (mesoscopic circuits, amorphous solids\textellipsis ). However only a few experiments [2,3] explored its more challenging limit when the quantum system is strongly coupled to the many degrees of freedom of the bath  despite numerous theoretical predictions. In this regime the ground state of the whole system is nontrivial: the spin is highly entangled with the bath, forming a manybody system. I will present a new architecture based on superconducting circuits to tackle this challenging problem. It offers two main advantages: first it allows to reach the ultrastrong coupling between the quantum system and its bath; second one can experimentally monitor the qubit and its bath at the same time, and thus reveal the manybody correlations which are building up when all the degrees of freedom become entangled. Our approach consists in coupling a superconducting artificial atom (namely a transmon qubit) to a metamaterial made of thousands of SQUIDs. The latter sustains many photonic modes and shows characteristic impedance close to the quantum of resistance. As a direct application, we use this circuit to explore quantum optics in the ultrastrong coupling regime, where new phenomena arise [47]. [1] Leggett, A. et al., Rev. Mod. Phys. 59(1), 1 (1987). [2] FornD\'{\i}az, P. et al., Nat. Phys. AOP (2016). [3] Haeberlein, M. et al., arXiv: 1506.09114 (2015). [4] Le Hur K., Phys. Rev. B 85, 140506(R) (2012). [5] Goldstein M. et al., Phys. Rev. Lett. 110, 017002 (2013). [6] Gheeraert N. et al., arXiv :1601.01545 (2015). [7] Yoshihara F. et al., Nat. Phys. AOP (2016). [Preview Abstract] 
Monday, March 13, 2017 12:27PM  1:03PM 
B19.00003: Timeresolved observation of thermalization in an isolated quantum system Invited Speaker: Tobias Schaetz Starting from which size can a closed quantum system feature thermailization, how can we reveal and interpret the related microscopic dynamics? We want to discuss our experimental study based on linear chains of up to five trapped ions using two different isotopes of magnesium to realize a single spin with tunable coupling to a resizable bosonic environment. By that we extend our trappedion system including its engineered phonon environment up to relevant Hilbert space dimensions. We measure time averages and fluctuations of spin observables and exploit an effective dimension to study their dependence on the size of the system. We find time averages of spin observables becoming indistinguishable from microcanonical ensemble averages, and amplitudes of time fluctuations decaying as we increase the effective system size. Simultaneously, we monitor the coherent dynamics, revealing the importance of initial and transient time scales by direct observation of the evolution towards thermal equilibrium. We interpret this behaviour as the emergence of statistical mechanics in a nearperfectlyisolated quantum system, despite its seemingly small size. In general, trappedion are well suited to study quantum dynamics at a fundamental level, featuring unique control in preparation, manipulation, and detection of electronic and motional degrees of freedom. Their Coulomb interaction of long range permits tuning from weak to strong coupling to the environment and controlling nonlinear contributions. Additionally, systems can be scaled bottom up to the mesoscopic size of interest to investigate manybody physics. We aim to discuss future prospects, such as, generating a multitude of initial conditions, choosing different system and environment states, and preparing initial correlations. The system allows measuring a variety of observables. Applying those techniques, we can study, e.g., nonMarkovianity of the dynamics, which is evidenced already by revivals in the evolution. [Preview Abstract] 
Monday, March 13, 2017 1:03PM  1:39PM 
B19.00004: Interacting ManyBody Spin Systems that Fail to Quantum Thermalize Invited Speaker: Phil Richerme This talk will describe the experimental observation of two mechanisms  manybody localization (MBL) and prethermalization  that prevent interacting quantum systems from attaining thermal equilibrium. Effective magnetic spins are encoded within the longcoherencetime electronic states of trapped ions, which are measured with nearly perfect efficiency. Tunable, longrange interactions are generated across the entire chain using statedependent optical dipole forces. MBL states are created by applying random, sitedependent disorder in the presence of a longrange interacting Ising Hamiltonian, while prethermal states arise in the presence of a longrange interacting XYmodel Hamiltonian. In both scenarios, the system retains strong memory of its initial conditions and cannot be welldescribed by equilibrium statistical mechanics. This trappedion platform can be scaled to higher numbers of spins, where detailed modeling of MBL or prethermal behavior becomes impossible due to the complexity of representing such highly entangled quantum states. [Preview Abstract] 
Monday, March 13, 2017 1:39PM  2:15PM 
B19.00005: Quantum magnetism in different AMO systems. Invited Speaker: Ana Maria Rey One of the most important goals of modern quantum sciences is to learn how to control and entangle manybody systems and use them to make powerful and improved quantum devices, materials and technologies. However, since performing full state tomography does not scale favorably with the number of particles, as the size of quantum systems grow, it becomes extremely challenging to identify, and quantify the buildup of quantum correlations and coherence. In this talk I will report on a protocol that we have developed and experimentally demonstrated in a trapped ion quantum magnet in a Penning trap, which can perform quantum simulations of Ising spin models [1,2]. In those experiments strong spinspin interactions can be engineered through optical dipole forces that excite phonons of the crystals. The number of ions can be varied from tens to hundreds with high fidelity control. The protocol uses time reversal of the manybody dynamics, to measure outoftimeorder correlation functions (OTOCs). By measuring a family of OTOCs as a function of a tunable parameter we obtain finegrained information about the state of the system encoded in the multiple quantum coherence spectrum, extract the quantum state purity, and demonstrate the buildup of up to 8body correlations. We also use the protocol and comparisons to a full solution of the master equation to investigate the impact of spinmotion entanglement and decoherence in the quantum dynamics. Future applications of this protocol could enable studies of manybody localization, quantum phase transitions, and tests of the holographic duality between quantum and gravitational systems. [1] J. G. Bohnet, B. C. Sawyer, J.W. Britton, M. L. Wall, A. M. Rey, M. FossFeig, John J. Bollinger, Science 352, 1297 (2016). [2] M G\"{a}rttner, J G. Bohnet, A SafaviNaini, M. L. Wall, J. J. Bollinger and A.M. Rey, arXiv:1608.08938 [Preview Abstract] 
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