Session J04: Quantum simulation I

Probing the Lipkin-Meshkov-Glick model with ultracold Dysprosium atoms

In this talk, we will report the study of the Lipkin-Meshkov-Glick model, induced by near-resonant light coupling to the J$=$8 ground state of an ultracold cloud of Dysprosium. We investigate the paramagnetic to ferromagnetic phase transition expected from this model, making a full characterisation of the ground state properties as well as a quantitative study of the dynamics of the quantum critical regime. Due to the large value of J, a good qualitative agreement is found, away from the phase transition, with mean-field predictions.   

Quantum simulation with two dimensional Wigner crystal in monolithic ion trap

We report adiabatic quantum simulation with two dimensional crystals of ions. Our trap is a three-dimensional monolithic Paul trap, where we can generate the pan-cake type of 2 dimensional harmonic potential by squeezing only one of the radial frequency with proper principle axis. We observe the two dimensional Wigner crystal of ions, where the direction of main micromotion is perpendicular to the net-propagation vector of Raman laser beams, which allows us to perform coherent quantum operation without serious problem of micromotion. By shinning Raman beams of 355 nm laser on the crystal, we generate the Ising type interaction between ions. We perform the adiabatic ground state preparation of the transverse Ising model and observe different character of the ground state with various number of ions. Moreover, we can control the connection graph of the Ising interaction by using different motional sidebands. Our work would open a new path for quantum simulation.   

Digital and analog simulation of para-particles

A para-oscillator is a parity-deformed harmonic oscillator characterized by an order parameter. This generalizes the standard Fermi-Dirac and Bose-Einstein statistics associated with fermions and bosons to para-particles. We realize a method for simulating and characterizing these alternative particles using a trapped ion experiment. The combination of the Jaynes-Cummings and anti-Jaynes Cummings dynamics present in a trapped ion coupled to multiple modes of motion simultaneously allows us to recover effective Hamiltonians which create a system analogous to para-Fermi or para-Bose oscillators. Trapped ions are a versatile quantum simulator and a main contender for a universal circuit model quantum computer. We use both of these flavors in this project, simulating para-Bosons digitally using Trotterization and para-Fermions directly by tailoring the native ion-mode couplings. We discuss the mapping steps and the latest experimental results.   

Single photon Chern insulator with superconducting microwave lattices

We present the latest progress in developing a new architecture for exploration of topological quantum matter. We construct microwave photonic lattices from tunnel-coupled, time-reversal-broken microwave cavities that are both low loss and compatible with Josephson junction-mediated photon-photon interactions, allowing us access to topological phenomena such as the fractional quantum Hall effect. We employ seamless 3D microwave cavities all machined from a single block of niobium, so our meta-material is scalable and directly compatible with the cQED toolbox, as it is composed only of niobium for the cavities, plus Yttrium-Iron-Garnet (YIG) spheres and Neodymium magnets to produce the synthetic magnetic field. After observing topologically protected chiral edge states with microsecond lifetimes circling the superconducting lattice, we are now coupling the Josephson junction qubits to lattice sites in order to add nonlinearity and particle interactions.   

Exploring synthetic quantum matter in superconducting circuits

Superconducting circuits have emerged as a competitive platform for quantum computation because they offer controllability, long coherence times and strong interactions. Here we apply this toolbox to explore strongly correlated quantum matter by building a Bose–Hubbard lattice for photons in the strongly interacting regime. We develop a versatile method to prepare incompressible many-body phases using engineered dissipation and apply it to our system to stabilize a Mott insulator of photons against losses. Site- and time-resolved readout of the lattice allows us to investigate the microscopic details of the thermalization process through the dynamics of defect propagation and removal in the Mott phase. Our experiments demonstrate the power of superconducting circuits for studying strongly correlated matter in both coherent and engineered dissipative settings. Future prospects include the exploration of strongly correlated topological matter and quantum thermodynamics.   

Driven Dissipative Stabilization of a Photonic Mott-insulator

The rich physics of strongly-correlated quantum materials can be explored in synthetic systems built with microwave photons in superconducting circuits in the circuit QED paradigm. However, even the minimal intrinsic loss present in photonic platforms makes many-body quantum state preparation a unique challenge. We build a 1D Bose-Hubbard lattice for photons where capacitively coupled transmon qubits serve as lattice sites, and the transmon anharmonicity corresponds to strong photon-photon interaction. We employ reservoir engineering to dissipatively stabilize a n$=$1 Mott insulator. Site-resolved microscopy allow detailed studies of the thermalization process through the dynamics of defect propagation and removal in the Mott phase. Recent improvements to our experiment will allow us to probe multi-site correlations - potentially revealing the intricate interplay of correlations, entanglement and thermalization in these driven-dissipative systems. We explore prospects for employing this platform to stabilize topological quantum phases of light and probe their thermodynamics.   

Hybrid Quantum-Classical QAOA Quantum Simulation with Trapped Atomic Ions

Hybrid quantum-classical algorithms, such as quantum approximate optimization algorithms (QAOA)\footnote{E. Farhi et al., arXiv:1411.4028v1}, are a promising tool to provide an approximate set of solutions to combinatorial optimization problems and to prepare non-trivial quantum states\footnote{W. W. Ho \& T. H. Hsieh, arXiv:1803.00026v3}. Here we report the implementation of a shallow-depth QAOA protocol with trapped atomic ions to compute the ground state energy of the transverse field Ising model with tunable long-range interactions. We performed an exhaustive search of the variational parameters to optimize the algorithm and investigated its performance as a function of system size. We plan to interface our quantum simulator with a classical optimization algorithm to find a set of parameters that minimize the energy output of QAOA.   

Confined Dynamics of a Linear Spin Chain After a Quench using a Trapped Ion Quantum Simulator

Trapped-ion quantum simulators are pristine quantum platforms to investigate out-of-equilibrium many-body systems. Here we report an experimental study of the dynamics in a transverse field Ising model with tunable long range interactions after a quantum quench [1, 2]. We observe a regime in which the spreading of correlations is bounded and the magnetization dynamics is a direct probe of~low energy quasi-particle excitation~confinement [3].~The experiment is explained using a `two kink' model, which considers a linear spin chain with only two domain walls [4]. We plan to extend this experiment by looking directly at spin correlation propagation and to look at finite size scaling effects by performing the experiment with longer ion chains. [1] P. Richerme, et al, \textit{Nature}~\textbf{volume511},~pages198--201~(10 July 2014) [2] J. Zhang, et al,\textit{ Nature}~\textbf{volume551},~pages601--604~(30 November 2017) [3] M. Kormos, et al,\textit{ Nature Physics}~\textbf{volume13},~pages246--249~(2017) [4] F. Liu, et al, arXiv:1810.02365   

Quantum nonlinear dynamics of collective spin models using measurement-based feedback control in ultracold atoms

We propose a measurement-based feedback scheme to control the collective spin dynamics of an ultracold atomic ensemble. The protocol consists of a weak (unsharp) measurement of one component of the collective spin followed by feedback in which an unitary evolution is applied conditioned on the measurement outcome. By proper choice of the feedback policy and measurement strength, we can simulate basic paradigms of quantum nonlinear dynamics including the chaotic Kicked Top and the Lipkin-Meshkov-Glick (LMG) model. We develop an analytical description of the dynamics under the Gaussian approximation, and explicitly show that, by an appropriate choice of the feedback, the regular, mixed and chaotic classical features of the classical Kicked Top phase space emerge from the noisy dynamics as the size of the spin ensemble increases. We characterize the chaos by studying the corresponding classical Lyapunov exponents. Through an appropriate feedback policy, in a Trotter-like fashion our protocol can recover the classical LMG model, with the well-known bifurcation process. We characterize this dynamics by performing an adiabatic passage and study the implications for robust quantum simulation   

Quantum simulation of Unruh radiation in a curved spacetime

We demonstrate a new approach to simulate quantum many-body systems in a non-inertial frame by parametric modulation of interactions; based on the equivalence principle, the system is effectively in a curved spacetime. Starting with a Bose-Einstein condensate, we periodically modulate the atomic interactions near a Feshbach resonance. An outgoing, fluctuating matterwave field is observed, which faithfully simulates the thermal radiation of vacuum in a highly accelerating frame, predicted by W. Unruh in 1976. Despite the thermal behavior from statistical analysis, we further observe the long-range phase coherence and the temporal reversal of matterwave emission, confirming the quantum origin of the simulated Unruh radiation. Our demonstration offers a new avenue to investigate novel dynamics of quantum systems in a curved spacetime.