Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session L39: Superconducting Circuits and Quantum Simulation |
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Sponsoring Units: GQI Chair: Yu Chen, Google Inc. Room: 213AB |
Wednesday, March 4, 2015 8:00AM - 8:12AM |
L39.00001: Low-energy states in a chain of inductively coupled Josephson junctions Hendrik Meier, Richard T. Brierley, Angela Kou, Steven M. Girvin, Leonid I. Glazman We investigate a long chain of inductively coupled Josephson junctions penetrated by an external magnetic field. In the limit of infinite junction capacitances, we determine the classical ground state and find that the competition between Josephson and inductive forces leads to a rich phase phase diagram as a function of magnetic flux per plaquette $\phi_e$ and the ratio $\ell^2=E_J/E_L$ of Josephson ($E_J$) and inductive ($E_L$) energies. At large $\ell$, kinks in the superconducting phase set in as a function of $\phi_e$ similarly to vortices in type-II superconductors. Upon further increasing $\phi_e$, the interplay between kink-kink interaction and pinning on the lattice leads to a Frenkel-Kontorova-type (devil's) staircase of phases distinguished by different rational kink densities. At $\phi_e$ equal to half a flux quantum, the system bears similarity to a classical Ising antiferromagnet, possibly with a long-ranged exchange. Inclusion of a finite junction capacitances is similar to placing the Ising chain in a transverse magnetic field (the quantum Ising model). Using this similarity, we investigate the quantum dynamics of a chain of fluxonium qubits. [Preview Abstract] |
Wednesday, March 4, 2015 8:12AM - 8:24AM |
L39.00002: Ground states and excitations of inductively coupled fluxonium qubits R.T. Brierley, H. Meier, A. Kou, L.I. Glazman, S.M. Girvin We consider fluxonium qubits arranged in a one dimensional array, where the inductors are shared between neighboring qubits. For an infinite system with small charging energies, there are a series of different phases that depend on the applied magnetic flux and the ratio of the inductive and Josephson energies. For small flux and large Josephson energy, the behavior of the classical ground state is similar to the Frenkel-Kontorova model, while when the flux is half a flux quantum it is similar to an Ising antiferromagnet. A realistic finite system will not exhibit a phase transition but some features of the infinite-size limit should persist. We investigate theoretically the ground and low-lying excited states for experimentally relevant parameters. We discuss how the nature of the ground state changes, and what experimental signatures would be expected. [Preview Abstract] |
Wednesday, March 4, 2015 8:24AM - 8:36AM |
L39.00003: Reentrant Behavior in A Multi-connected Superconducting Jaynes-Cummings Lattice Lin Tian, Kangjun Seo Superconducting quantum devices have excellent connectivity, tunable coupling and long decoherence time as demonstrated by recent experiments. These devices provide a powerful platform for constructing analog quantum simulators to study novel many-body effects. Here we present a multi-connected Jaynes-Cummings lattice model, where the qubits and the resonators are connected alternatively. In a one-dimensional configuration, this model bears an intrinsic symmetry between the left and the right qubit-resonator couplings under a mirror reflection. Different from the coupled cavity array (CCA) model, the qubit-resonator couplings in this model induce both onsite Hubbard nonlinearity and hopping of the excitations along the lattice. By analyzing this model in the limiting cases of very different couplings, we show that this model demonstrates a Mott insulator--superfluid--Mott insulator transition at commensurate fillings with symmetric critical points. The reentry to the Mott insulator phase originates from the symmetry between the couplings. \\[4pt] [1] K. Seo and L. Tian, eprint arXiv:1408.2304. [Preview Abstract] |
Wednesday, March 4, 2015 8:36AM - 8:48AM |
L39.00004: Phase Diagram of A Multi-connected Superconducting Jaynes-Cummings Lattice at Commensurate and Incommensurate Fillings Kangjun Seo, Lin Tian A multi-connected superconducting Jaynes-Cummings lattice can be constructed with alternatively-connected superconducting qubits and resonators. In a one-dimensional configuration, this model bears an intrinsic symmetry between the left and the right qubit-resonator couplings. Here we study the quantum phase transition of this model using the exact diagonalization method. At commensurate fillings, the off-diagonal long range order of the single-particle density matrix and the energy gap are calculated. We obtain the phase diagram of this model, which demonstrates a symmetry between the couplings and a reentry to the Mott insulator phase. For a system with given chemical potential, the density of the excitations contains integer-valued plateaus between critical chemical potentials that define the boundaries of different many-body phases and indicate the phase transition. We also discuss the implementation of this model with superconducting devices, including the state preparation and detection schemes. \\[0pt] [1] K. Seo and L. Tian, eprint arXiv:1408.2304. [Preview Abstract] |
Wednesday, March 4, 2015 8:48AM - 9:00AM |
L39.00005: Simulating an Interacting Quantum Gas with Superconducting Circuits Christopher Eichler, Jonas Mlynek, Jonas Butscher, Philipp Kurpiers, Tobias Osborne, Andreas Wallraff The high level of control achievable over quantized degrees of freedom have turned superconducting circuits into one of the prime physical architectures for quantum computing and simulation. While conventional approaches towards quantum information processing mostly rely on unitary time evolution, more recently open-system dynamics are considered for quantum simulations. In this talk, I will present experiments in which we use an open cavity QED system with tunable interactions to simulate the ground state of an interacting Bose gas confined in one dimension [1,2]. These experiments rely on the ability to efficiently measure higher order photon correlations of the cavity output field. For this purpose we have developed a quantum limited amplifier achieving phase-preserving amplification at large bandwidth and high dynamic range [3]. Our results explore a different path towards the simulation of complex quantum many-body physics based on the controlled generation and detection of nonclassical radiation in an open quantum system.\newline [1] S. Barrett et al., Phys. Rev. Lett. 110, 090501 (2013).\newline [2] F. Verstraete and J. I. Cirac, Phys. Rev. Lett. 104, 190405 (2010).\newline [3] C. Eichler et al., Phys. Rev. Lett. 113, 110502 (2014). \newline [Preview Abstract] |
Wednesday, March 4, 2015 9:00AM - 9:12AM |
L39.00006: Many-body localization in a quantum system subject to a local periodic drive Canran Xu, Maxim Vavilov We consider a one dimensional spin chain system with quenched disorder and in the presence of a local harmonic drive. We study the time evolution of the system in the Floquet basis and evaluate the Bures displacement of the system in the Hilbert space caused by the drive per one period. This displacement can be used to identify two phases of the system: (1) the many-body localized phase, in which the distribution of the distance exhibits long tails while its average value decreases rapidly as disorder increases; and (2) the ergodic phase, in which the displacement distribution is narrow and its average value weakly depends on disorder. This distinction in the average value of the displacement between the two phases develops readily for system with ten or more spins. Therefore, recently built networks of superconducting qubits subject to a local microwave drive can simulate dynamics of a system in the many-body localization regime. [Preview Abstract] |
Wednesday, March 4, 2015 9:12AM - 9:24AM |
L39.00007: Localization vs. delocalization of waves in circuit QED Bruno G. Taketani, Frank K. Wilhelm Wave localization in disordered media is an important phenomenon arising from the destructive interference of waves from the many scatterers in the medium. However, interaction between localized modes may counteract this effect and lead to a localization-delocalization transition. Understanding this interplay between disorder and interaction is thus of great importance. We investigate this interplay using quasiperiodic JJAs. This metamaterial possesses degenerate localized modes coexisting with delocalized modes which can be made to interact via the junctions Kerr non-linearity. On the quantum regime, the system presents a natural route to generate photon-photon interaction in circuit QED. The proposed experiment can be readily made with current technologies. [Preview Abstract] |
Wednesday, March 4, 2015 9:24AM - 9:36AM |
L39.00008: Site-wise manipulations induced phase transitions of interacting photons using superconducting circuit simulators Xiuhao Deng, Chunjing Jia, Chih-Chun Chien The Bose Hubbard model (BHM) of interacting bosons in a lattice has been a paradigm in many body physics. Here a quantum simulator of the BHM using a superconducting circuit is proposed. Specifically, a superconducting transmission line resonator supporting microwave photons is coupled to a charge qubit to form one site of the BHM, and adjacent sites are connected by a tunable coupler. To obtain a mapping from the superconducting circuit to the BHM, we focus on the dispersive regime where the excitations remain photon-like. Standard perturbation theory is implemented to locate the parameter range where the BHM can be simulated. This simulator allows single-site manipulations and we illustrate this feature by considering two scenarios where a single-site manipulation can drive a Mott insulator-superfluid transition. The critical point of the transition can be located by mean-field analyses and the exact diagonalization method was implemented to provide accurate results. The variance of the density and the fidelity metric clearly show signatures of this transition. Experimental realizations and other possible applications of this simulator are also discussed. [Preview Abstract] |
Wednesday, March 4, 2015 9:36AM - 9:48AM |
L39.00009: Classical chaos and its correspondence in superconducting qubits C. Neill, B. Campbell, Z. Chen, B. Chiaro, A. Dunsworth, M. Fang, I. Hoi, J. Kelly, A. Megrant, P. O'Malley, C. Quintana, A. Vainsencher, J. Wenner, T. White, R. Barends, Yu Chen, A. Fowler, E. Jeffrey, J. Mutus, P. Roushan, D. Sank, J.M. Martinis Advances in superconducting qubits have made it possible to experimentally investigate quantum-classical correspondence by constructing quantum systems with chaotic classical limits. We study the quantum equivalent of a classical spinning top using three fully coupled qubits that behave as a single spin-3/2 and subject the spin to a sequence of non-linear rotations. The resulting entanglement bears a striking resemblance to the classical phase space, including bifurcation, and suggests that classical chaos manifests itself as quantum entanglement. Studying the orientation of the spin-3/2 reveals that the rotations which generate chaos and entanglement are at the same time the source of disagreement between the quantum and classical trajectories. Our experiment highlights the correspondence between classical non-linear dynamics and interacting quantum systems. [Preview Abstract] |
Wednesday, March 4, 2015 9:48AM - 10:00AM |
L39.00010: Quantum simulation with arrays of transmon qubits: Ising dynamics Vinay Ramasesh, Shay Hacohen-Gourgy, Thomas Kiendl, Florian Marquardt, Nathan Siwak, Christopher Richardson, Irfan Siddiqi Chains of coupled qubits are known to realize the transverse-field Ising Hamiltonian in the two-level approximation. In this model, the qubit transition frequencies map onto the external magnetic field, so the ground and excited states play the role of spin-up and spin-down atoms. We implement this structure in a planar, on-chip architecture, with a one dimensional linear array of capacitively-coupled transmon qubits, where the two terminal qubits are dispersively coupled to microwave independent resonators for state readout. We present spectroscopic data and describe coherent manipulations in the array. [Preview Abstract] |
Wednesday, March 4, 2015 10:00AM - 10:12AM |
L39.00011: Quantum simulation with an array of transmon qubits: Bose-Hubbard model Shay Hacohen-Gourgy, Vinay Ramasesh, Claudia De Grandi, Steven Girvin, Irfan Siddiqi Chains of capacitively-coupled transmons can emulate the Bose-Hubbard Hamiltonian when one considers the full level-structure of the circuit. Here, each individual transmon plays the role of a lattice site, with the excitation level of each transmon corresponding to the number of bosons occupying that particular site. The transmon's anharmonicity gives rise to the attractive contact-interaction term, while the capacitive coupling realizes the hopping amplitude. We implement such a chain of 3 capacitvely-coupled transmons in a single 3D microwave cavity. In our parameter regime, the ground state of the 3-excitation subspace is one in which all excitations lie on a single qubit. Using cavity-assisted bath engineering, it should be possible to cool from an initial state in this subspace to the ground state. We present the current status of this goal. [Preview Abstract] |
Wednesday, March 4, 2015 10:12AM - 10:24AM |
L39.00012: Perturbative scanning probe microscopy on a Kagome lattice of superconducting microwave resonators Devin Underwood, Will Shanks, Andy C.Y. Li, Jens Koch, Andrew Houck Microwave photons confined to a lattice of coupled resonators, each coupled to its own superconducting qubit have been predicted to exhibit matter like quantum phases. Realizing such a lattice-based quantum simulator presents a daunting experimental challenge; as such, new tools and measurement techniques are a necessary precursor. Here, we present measurements of the internal mode structure of microwave photons on a 49-site Kagome lattice of capacitively coupled coplanar waveguide resonators without qubits. By scanning a probe with a sapphire tip over the surface of a single lattice site, the resonant frequency was detuned, thus forming a local defect in the lattice. This perturbation resulted in measurable shifts in the lattice spectrum, which were used to extract the mode weights at the perturbed site. By perturbing each lattice site it was possible to reconstruct a complete map of different normal mode weights within the entire lattice. Additionally we present experimental evidence of a frustrated flat band that arises from the Kagome lattice geometry. [Preview Abstract] |
Wednesday, March 4, 2015 10:24AM - 10:36AM |
L39.00013: Perturbative study of interacting photons in open lattices Andy C.Y. Li, Francesco Petruccione, Jens Koch Quantum simulation realized in the circuit QED architecture is an emerging direction to study many-body physics in open lattice systems. Among several models of interacting photons, the driven-dissipative Jaynes-Cummings (JC) lattice is commonly employed to investigate the steady-state and dynamical behavior. While there is a wealth of analytical and numerical tools applicable to closed lattice systems in thermal equilibrium, the number of methods to treat open lattice systems is rather limited. Hence, many properties of open lattices remain an open question. Here, we formulate a general perturbation theory and an infinite-order resummation scheme applicable to open lattices. We then apply this theory to the driven-dissipative JC lattices to predict steady-state expectation values. This allows us to explore the rich features due to photon-qubit interaction and compare results obtained for finite chains and infinite lattices. [Preview Abstract] |
Wednesday, March 4, 2015 10:36AM - 10:48AM |
L39.00014: Experimental Study of a Disordered Jaynes-Cummings Lattice Mattias Fitzpatrick, Devin Underwood, Darius Sadri, Jens Koch, Andrew Houck Circuit quantum electrodynamics (cQED) is an exciting testbed for simulation of open quantum systems. Effective photon-photon interactions can be mediated by a superconducting qubit strongly coupled to a microwave transmission line cavity. Many-body quantum simulators can be realized using Jaynes-Cummings lattices, where a competition is induced between onsite interactions and hopping between sites. In this experiment, we present measurements of a Kagome lattice consisting of 49 microwave cavity resonators and 49 transmon qubits. We fabricate each qubit with random area superconducting quantum interference devices (SQUIDs) to create qubits with different sensitivity to magnetic field. This allows us to simultaneously tune all of the qubits randomly with the application of a single external magnetic field, enabling a systematic study of the effects of disorder. We will present preliminary experimental results from this Kagome lattice as well as future directions of quantum simulation using Jaynes-Cummings lattices. [Preview Abstract] |
Wednesday, March 4, 2015 10:48AM - 11:00AM |
L39.00015: Experimental investigation of a steady-state dynamical phase transition in a Jaynes-Cummings dimer James Raftery, Darius Sadri, Stephan Mandt, Hakan T\"ureci, Andrew Houck Experimental progress in circuit-QED has made it possible to study non-equilibrium many-body physics using strongly correlated photons. Such open and driven systems can display new types of dynamical phase transitions [1]. Recently, a novel steady state transition has been predicted for a Jaynes-Cummings dimer where the photon current between the two cavities acts as an order parameter [2]. Here, we discuss the theory and report measurements of the steady-state behavior of a circuit-QED dimer with in situ tunable inter-cavity coupling and on-site photon-photon interaction. [1] J. Raftery, D. Sadri, S. Schmidt, H. E. T\"ureci, and A. A. Houck, Phys. Rev. X 4, 031043 (2014). [2] S. Mandt, D. Sadri, A. A. Houck, and H. E. T\"ureci, arXiv:1410.3142 (2014). [Preview Abstract] |
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