Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session D35: Focus Session: Superconducting Qubits: Simulation & Annealing 
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Sponsoring Units: GQI Chair: Jay Gambetta, IBM Room: 702 
Monday, March 3, 2014 2:30PM  3:06PM 
D35.00001: Catch and Release of Microwave Photons Invited Speaker: Yi Yin Quantum information is often encoded in photons, which can both propagate freely along transmission lines and be stored in cavity resonators. To store photons efficiently, the resonator should have negligible coupling with the outside world. On the other hand, the resonator should be strongly coupled to a transmission line through which photons can be transmitted and received. These contrary requirements can be resolved with adjustable coupling. We experimentally demonstrate a superconducting resonator with variable coupling to a measurement transmission line. The resonator coupling can be adjusted through zero to a photon emission rate 300 times the intrinsic resonator decay rate. We demonstrate the catch and shaped release of microwave photons as well as the control of nonclassical Fock states. We achieve a highfidelity catch efficiency (99.4{\%}) for a ``timereversed'' shaped photon. These results will enable high fidelity quantum state transfer between distant cavities. [Preview Abstract] 
Monday, March 3, 2014 3:06PM  3:18PM 
D35.00002: Imaging the mode structure of a kagome lattice of superconducting resonators with a scanning defect Devin Underwood, Will Shanks, Andy C.Y. Li, Jens Koch, Andrew Houck It has been theoretically shown that a lattice of coupled electromagnetic cavities each strongly coupled to a twolevel system exhibit quantum phase transitions of polaritons. Such a system consists of a lattice of coupled sites each described by the JaynesCummings Hamiltonian. The circuit quantum electrodynamics architecture is a natural choice for such experiments because of the ease of fabrication, and the easily obtainable strong coupling limit. In these systems an important first step is to build and understand a large photonic lattice of microwave resonators without qubits. Here we present measurements of the mode structure of microwave photons in an array of 49 niobium CPW resonators that are capacitively coupled to form a kagome lattice. Our method for extracting the mode structure is a piece of sapphire mounted to a threeaxis positioning stage that we bring into contact with each resonator. This scanning defect locally perturbs each lattice site and the shifted transmission spectrum can then be used as a metric to extract the internal mode structure. When compared to calculations from a tight binding Hamiltonian, measured modes show good agreement. These results demonstrate our ability to fabricate and understand large lattices of microwave resonators. [Preview Abstract] 
Monday, March 3, 2014 3:18PM  3:30PM 
D35.00003: CircuitQEDbased superconducting quantum simulator for the Holsteinpolaron model Feng Mei, Vladimir Stojanovi\'{c}, Irfan Siddiqi, Lin Tian We propose an analog quantum simulator for the Holstein molecularcrystal model based on a superconducting circuitQED system in the dispersive regime. The manybody Hamiltonian of this model includes both bosonic and fermionic degrees of freedom. By varying the driving field on the superconducting resonators, one can readily access both the adiabatic and antiadiabatic regimes of this model, and reach the strong eph coupling limit required for smallpolaron formation. We show that smallpolaron state of arbitrary quasimomentum can be generated by applying a microwave pulse to the resonators. We also show that significant squeezing in the resonator modes can be achieved in the polaroncrossover regime through a measurementbased scheme. [Preview Abstract] 
Monday, March 3, 2014 3:30PM  3:42PM 
D35.00004: Dynamics of macroscopic quantum selfbound states in arrays of transmon qubits Claudia De Grandi, Steven M. Girvin We consider the manybody physics of an array of transmon qubits in a cavity. Due to the negative anharmonicity and the exchange coupling between the qubits, such a system realizes a BoseHubbard model with attractive interactions and thus the $N$excitation manifold is expected to have selfbound states. We study the existence of such macroscopic states in the onedimensional case with open boundary conditions as a function of the parameters of the model, comparing the classical and the quantum predictions. We then analyze the dynamics of the selfbound states in the experimentally relevant scenario of an open dissipative system, where the qubits have a finite energy relaxation time $T_1$. We numerically simulate the dynamics with a quantum trajectory approach supported by a Lanczos diagonalization procedure. [Preview Abstract] 
Monday, March 3, 2014 3:42PM  3:54PM 
D35.00005: Detecting elementary excitations of a quantum simulator with superconducting resonator Lianghui Du, J.Q. You, Lin Tian Analog quantum simulators can emulate various manybody systems and can be used to study novel quantum correlations in such systems. One essential question in quantum simulation is how to detect the properties of the simulated manybody system, such as ground state property and spectrum of elementary excitations. Here we present a circuit QED approach for detecting the excitation spectrum of a quantum simulator by measuring the correlation spectrum of a superconducting resonator. For illustration, we apply this approach to a simulator for the transverse field Ising model coupling to a coplanar waveguide resonator. The simulator can be implemented with an array of superconducting flux qubits. We show that the resonance peaks in the correlation spectrum reveal exactly the frequencies of the excitations. [Preview Abstract] 

D35.00006: ABSTRACT WITHDRAWN 
Monday, March 3, 2014 4:06PM  4:18PM 
D35.00007: Simulating quantum field theories with superconducting circuits Antonio Mezzacapo, Guillermo Romero, Laura Garc\'Ia\'Alvarez, Jorge Casanova, Lucas Lamata, Enrique Solano In this contribution, we present the quantum simulation of fermionic field modes interacting via a continuum of bosonic modes with superconducting circuits. Unlike many quantum technologies, superconducting circuits offer naturally the continuum of bosonic modes by means of onedimensional transmission lines. In particular, we consider a simplified version of 1+1 quantum electrodynamics (QED), which may describe Yukawa interactions, and the coupling of fermions to the Higgs field. Our proofofprinciple proposal is designed within the stateoftheart circuit QED technology, where fermionic fields are encoded in superconducting flux qubits, in a scalable approach that may lead to a fullfledged quantum simulation of quantum field theories. [Preview Abstract] 
Monday, March 3, 2014 4:18PM  4:30PM 
D35.00008: Digital Quantum Simulation of Heisenberg SpinSpin Interactions with Superconducting Qubits Y. Salathe, M. Mondal, P. Kurpiers, M. Oppliger, L. Steffen, S. Filipp, A. Wallraff, A. Mezzacapo, U. Las Heras, L. Lamata, E. Solano A major application of a scalable quantum computer is the simulation of intricate quantum systems, including spin models, which cannot be carried out efficiently on classical computers for more than a few tens of qubits. The Heisenberg model describes a spin system that cannot be obtained directly from available interactions in circuit QED. Nevertheless, it can be achieved by a stroboscopic decomposition in terms of elementary gates in a digital quantum simulation approach. In our experiments, we digitally simulate a system of two spin1/2 particles interacting via an isotropic Heisenberg XYZ interaction in the circuit QED architecture. The XYZ interaction is decomposed into a set of discrete twoqubit gates based on the exchange interaction mediated by the dispersive coupling of both qubits to a common cavity mode. The state evolution during the simulation is analyzed tomographically after each step for varying interaction strengths. This technique can be extended to general spin models, such that our experiments represent a first step towards the digital quantum simulation of larger spin systems with controllable lattice topology. [Preview Abstract] 
Monday, March 3, 2014 4:30PM  4:42PM 
D35.00009: Transmonbased simulator of nonlocal electronphonon coupling: a platform for observing sharp smallpolaron transitions Vladimir Stojanovic, Eugene Demler, Mihajlo Vanevic, Lin Tian We propose an analog simulator for a onedimensional model with momentumdependent (nonlocal) electronphonon couplings of SuSchriefferHeeger and ``breathingmode'' types. The superconducting circuit behind this simulator entails an array of transmon qubits and microwave resonators. Using a microwavedriving based protocol, smallpolaron Bloch states with arbitrary quasimomentum can be prepared in this system within times several orders of magnitude shorter than the qubit decoherence time. We show that  by varying the circuit parameters  one can readily reach the critical coupling strength for observing the sharp transition from a nondegenerate singleparticle ground state at zero quasimomentum ($K_{\textrm{gs}}=0$) to a twofold degenerate smallpolaron ground state corresponding to equal and opposite (nonzero) quasimomenta $K_{\textrm{gs}}$ and $K_{\textrm{gs}}$. Through exact diagonalization of our effective model, we show how this nonanalyticity is reflected in the relevant singleparticle properties (groundstate energy, quasiparticle residue, average number of phonons). Our work paves the way for understanding the physical implications of strongly momentumdependent electronphonon interactions. [Preview Abstract] 
Monday, March 3, 2014 4:42PM  4:54PM 
D35.00010: Simulating systems of itinerant spincarrying particles using arrays of superconducting qubits and resonators Sahel Ashhab We propose potential setups for the quantum simulation of itinerant spincarrying particles in a superconducting qubitresonator array. These proposals include the use of multiple polariton branches, multiple resonator modes and multiple qubits coupled to each resonator. We argue that a combination of using multiple qubits and multiple resonator modes is a promising route in this context, allowing the simulation of external magnetic fields and various forms of spindependent intersite hopping, including spinorbit coupling. This proposal could be implemented in stateoftheart superconducting circuits in the near future. [Preview Abstract] 
Monday, March 3, 2014 4:54PM  5:06PM 
D35.00011: Quantum Simulation with Arrays of Transmon Qubits Shay HacohenGourgy, Vinay Ramasesh, Oliver Viehmann, Jan von Delft, Florian Marquardt, Irfan Siddiqi We present progress toward quantum simulation of onedimensional spin chains using planar transmon qubits in a circuit QED architecture. In particular, we discuss the Ising model as realized by an array of capacitivelycoupled transmon qubits with the terminal qubit dispersively coupled to a microwave resonator. We engineer an approximation to the Ising Hamiltonian with the ground and excited states playing the role of spinup and spindown atoms. We present preliminary spectroscopic data and coherent manipulations in chains of varying length. [Preview Abstract] 
Monday, March 3, 2014 5:06PM  5:18PM 
D35.00012: Novel Architecture for High Speed and High Fidelity Readout of a Quantum Annealing Processor Fabio Altomare, Andrew J. Berkley, Richard Harris, Emile M. Hoskinson, Mark W. Johnson, Trevor M. Lanting, Sergey Uchaikin, Jed D. Whittaker, Paul Bunyk, Elena Tolkacheva, Ilya Perminov Hysteretic dc SQUIDs provide an easy method to read the state of hundreds of qubits\footnote{Supercond. Sci. Technol. \textbf{23}, 105014 (2010)}. However, this approach becomes impractical for circuits with an even larger number of qubits due to heating when dc SQUIDs switch, the relatively slow retrapping dynamics of high quality devices, and suboptimal scaling of the number of control lines with increasing numbers of qubits. The DWave Two processor uses an architecture that addresses all three of these issues. This new architecture makes use of Quantum Flux Parametron based shift registers that transfer the classical information produced as the output of the quantum annealing algorithm to a small number of fast nondissipative and high fidelity microwave readout devices. We will provide an introduction to our implementation, and present data pertaining to readout performance from a 512qubit quantum annealing processor. [Preview Abstract] 
Monday, March 3, 2014 5:18PM  5:30PM 
D35.00013: Programmable flux DACs in a Quantum Annealing Processor Emile M. Hoskinson, Fabio Altomare, Andrew J. Berkeley, Paul Bunyk, Richard Harris, Mark W. Johnson, Trevor M. Lanting, Elena Tolkacheva, Ilya Perminov, Sergey Uchaikin, Jed D. Whittaker Programming the DWave Two processor to solve a given problem involves adjustment of thousands of independent flux biases. This is accomplished with an array of 4480 onchip digitaltoanalog converters (DACs), addressed using 56 external lines. Each DAC comprises a superconducting loop and control circuitry that allows injection of a deterministic number of flux quanta, up to a maximum value determined by the device parameters and the addressing scheme. Indepth characterization is performed to determine DAC transferfunctions and the addressing levels needed for fast and reliable programming. In contrast with traditional singlefluxquanta (SFQ) circuitry, zero static power during programming is dissipated onchip, allowing efficient operation at mK temperatures. [Preview Abstract] 
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