Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session J28: Superconducting Qubits: Topological Effects, Entanglement and EIT |
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Sponsoring Units: GQI Chair: Britton Plourde, Syracuse University Room: 601 |
Tuesday, March 4, 2014 2:30PM - 2:42PM |
J28.00001: The merge of superconducting qubits with topological superconductors: microwave transitions as a signature of coherent parity mixing effects Eran Ginossar, Eytan Grosfeld In this talk we will discuss the light-matter effects that could arise if Majorana fermions are added to a superconducting charge qubit. Coupling Majorana fermion excitations to coherent external fields is an important stepping stone towards their manipulation and detection. We argue that such a device could contribute to the spectroscopic detection of topological-superconductor Majorana excitations. We analyse the charge and transmon regimes of a topological nano-wire embedded within a Cooper-Pair-Box, where the superconducting phase difference is coupled to the zero energy parity states that arise from Majorana quasi-particles. We show that at special gate bias points, the microwave photon-qubit coupling can be switched off via quantum interference, and in other points it is exponentially dependent on the control parameter $E_J/E_C$. We propose that this type of device could perform as a high coherence four-level system in the superconducting circuits architecture with tunability of the coupling to photons, a coveted property which is difficult to achieve with regular devices. [Preview Abstract] |
Tuesday, March 4, 2014 2:42PM - 2:54PM |
J28.00002: Topological Quantum Espionage Chang-Yu Hou, Kirill Shtengel, Gil Refael Can one transfer information encoded in Majorana modes between two distinct platforms? Or must one read out the information before transferring it to a new medium? We explore this question, and find that not only can information be transfered, but in some cases a fermionic occupation number can be stored non-locally by Majorana modes localized in two distinct p-wave superconductors with opposite chirality, as long as some tunneling contact between the two exists. [Preview Abstract] |
Tuesday, March 4, 2014 2:54PM - 3:06PM |
J28.00003: Flux-controlled quantum computation with Majorana zero modes Timo Hyart, Bernard van Heck, Ion Cosma Fulga, Michele Burrello, Anton R. Akhmerov, Carlo W.J. Beenakker Majorana zero modes, exotic quasiparticles which are their own antiparticles, can be constructed out of electron and hole excitations in topological superconductors. Because widely separated Majorana zero modes can store quantum information nonlocally and their non-Abelian braiding statistics allows accurate quantum gates, Majorana zero modes offer a promise for topological quantum computation. The coupling of Majorana zero modes to superconducting transmon qubits permits braiding of Majoranas and readout operations by external variation of magnetic fluxes. We identify the minimal circuit for the demonstration of the non-Abelian Majorana statistics and discuss the possible limitations which might hinder the braiding operation. A key benefit of our approach is that the whole operation is performed at the electrical circuit level, without requiring local control of microscopic parameters. Finally, we take a longer term perspective and introduce the Random Access Majorana Memory, a scalable circuit that can perform a joint parity measurement on Majoranas belonging to a selection of topological qubits. Such multi-qubit measurements allow for the efficient creation of highly entangled states and simplify quantum error correction protocols by avoiding the need for ancilla qubits. [Preview Abstract] |
Tuesday, March 4, 2014 3:06PM - 3:18PM |
J28.00004: Exploring the Effect of Noise on the Berry Phase using circuit QED S. Berger, M. Pechal, A.A. Abdumalikov, C. Eichler, L. Steffen, A. Fedorov, A. Wallraff, S. Filipp The Berry phase is independent of both energy and time: it solely depends on the trajectory of the quantum system in state space, and is equipped with a certain degree of robustness against slow fluctuations [1,2]. By introducing artificial distortions in the path in state space, we measure the geometric contributions to the dephasing of an effective two-level system. Our experiments, realized with a microwave-driven superconducting qubit, demonstrate that only those fluctuations which deform the path cause geometric dephasing. A direct comparison with the path-independent dynamic phase reveals that the Berry phase is less affected by noise-induced dephasing in the adiabatic limit of long evolution times. \newline [1] G.~De Chiara and G.~M.~Palma, \emph{Phys.~Rev.~Lett.~}\textbf{91}, 090404 (2003) \newline [2] S.~Filipp \emph{et al.}, \emph{Phys.~Rev.~Lett.~}\textbf{102}, 030404 (2009) [Preview Abstract] |
Tuesday, March 4, 2014 3:18PM - 3:30PM |
J28.00005: Measuring the Chern Number of a Superconducting Qubit from Nonadiabatic Response M.D. Schroer, W.F. Kindel, M. Kolodrubetz, M. Sandberg, M.R. Vissers, D.P. Pappas, A. Polkovnikov, K.W. Lehnert The accumulation of Berry's phase in superconducting qubits under cyclical evolution has been well studied,\footnote{P. J. Leek \emph{et al.}, Science \textbf{318}, 5858 (2007)}$^,$\footnote{S. Berger \emph{et al.} PRA \textbf{87}, 060303(R) (2013)} typically requiring fully adiabatic evolution. We demonstrate an alternative means of accessing the topology of a qubit, based on nonadiabatic manipulation.\footnote{V. Gritsev and A. Polkovnikov, PNAS \textbf{109}, 6457 (2012)} Integrating the measured Berry curvature over the Bloch sphere yields the Chern number ($\mathrm{ch}_{\mathrm{I}}$), which we find to be quantized. By adding an effective static field to the qubit, we demonstrate a topological transition from $\mathrm{ch}_{\mathrm{I}} = 1$ to $\mathrm{ch}_{\mathrm{I}} = 0$. This simple example of extracting the Chern number may be easily scaled to larger systems. [Preview Abstract] |
Tuesday, March 4, 2014 3:30PM - 3:42PM |
J28.00006: Theory of implementation of an impedance-matched $\Lambda$ system in circuit QED Kazuki Koshino, Kunihiro Inomata, Tsuyoshi Yamamoto, Yasunobu Nakamura In one-dimensional optical setups, light-matter interaction is drastically enhanced by the interference between the incident and scattered fields. Particularly, in an impedance-matched $\Lambda$-type three-level system, which has two identical radiative decay rates from the top level and interacts with a semi-infinite one-dimensional field in reflection geometry, a single photon deterministically induces the Raman transition and switches the electronic state of the system. Here we theoretically investigate a circuit QED system composed of a driven superconducting qubit and a resonator in the dispersive regime. We show that the dressed states of this system constitute an impedance-matched $\Lambda$ system under a proper choice of the frequency and power of the qubit drive. When we apply a resonant probe field to this system, it is down-converted nearly perfectly after a single reflection as long as the probe power is sufficiently weak. This indicates a deterministic quantum dynamics induced by single photons, which is applicable, for example, to the detection of single microwave photons and the bidirectional quantum memory (swapping) between a microwave photon and a superconducting qubit. [Preview Abstract] |
Tuesday, March 4, 2014 3:42PM - 3:54PM |
J28.00007: Realization of an Impedance-Matched $\Lambda$ System Using an Artificial Atom Kunihiro Inomata, Kazuki Koshino, Yasunobu Nakamura, Zhirong Lin, William D. Oliver, Jaw-Shen Tsai, Tsuyoshi Yamamoto We realize an impedance-matched $\Lambda$-type three-level system using dressed states in a circuit QED system, where a superconducting flux qubit and a coplanar waveguide resonator are coupled capacitively. Under an appropriate choice of microwave frequency and intensity for the qubit drive, two radiative decay rates from the upper level to the lower two levels in the $\Lambda$ system become identical, and the impedance-matched $\Lambda$ system is realized. Perfect absorption and nearly deterministic down-conversion of the incident microwave photons are theoretically expected in this system. We experimentally observe that the incident microwave is perfectly absorbed and is down-converted by 64~MHz corresponding to detuning between the qubit transition and the qubit drive. The down-converted signal is amplified by a Josephson parametric amplifier, and the power spectrum is directly detected. The conversion efficiency of $\sim 75\%$ has been obtained. [Preview Abstract] |
Tuesday, March 4, 2014 3:54PM - 4:06PM |
J28.00008: Demonstration of Geometric Landau-Zener Interferometry in a Superconducting Phase Qubit Yang Yu, Xinsheng Tan, Zhentao Zhang, Shiliang Zhu, Danwei Zhang, Siyuan Han Geometric quantum manipulation and Landau-Zener interferometry have been separately explored in many quantum systems. Here we fill this gap by combining these two approaches in the study of the dynamics of a superconducting phase qubit. We propose and then experimentally demonstrate Landau-Zener interferometry based on pure geometric phases in this solid-state qubit. We observe the interference due to geometric phases accumulated in the evolution between two consecutive Landau-Zener transitions, while the dynamical phase is eliminated by a spin-echo pulse. Our numerical simulation results using measured energy relaxation and dephasing times agree well with the experimental results. The full controllability of the qubit population as a function of intrinsically fault-tolerant geometric phases provides a promising approach to fault-tolerant quantum computation. [Preview Abstract] |
Tuesday, March 4, 2014 4:06PM - 4:18PM |
J28.00009: Preparing Schrodinger cat states by parametric pumping Zaki Leghtas, Steven Touzard, Ioan Pop, Brian Vlastakis, Evan Zalys-Geller, Victor V. Albert, Liang Jiang, Luigi Frunzio, Robert J. Schoelkopf, Mazyar Mirrahimi, Michel H. Devoret Maintaining a quantum superposition state of light in a cavity has important applications for quantum error correction. We present an experimental protocol based on parametric pumping and Josephson circuits, which could prepare a Schrodinger cat state in a cavity. This is achieved by engineering a dissipative environment, which exchanges only pairs or quadruples of photons with our cavity mode. The dissipative nature of this preparation would lead to the observation of a dynamical Zeno effect, where the competition between a coherent drive and the dissipation reveals non trivial dynamics. Work supported by: IARPA, ARO, and NSF. [Preview Abstract] |
Tuesday, March 4, 2014 4:18PM - 4:30PM |
J28.00010: Stabilization of entanglement between remote transmon qubits Felix Motzoi, Mohan Sarovar, Birgitta Whaley Entanglement between remote qubits can be a valuable resource for scalable quantum computation and other quantum technologies. Here, we discuss non-unitary methods for generating and stabilizing such entanglement between remote superconducting qubits. While joint measurement of the qubits using a sequential probe allows for post-selected entanglement, adding feedback during the measurement conditioned on the outcome allows for deterministic entanglement. This can be supplemented or substituted for with reservoir engineering techniques, which allow for non-zero concurrence in the steady state even in the presence of dephasing. Both the dispersive and near-resonant regimes of circuit QED are analysed. [Preview Abstract] |
Tuesday, March 4, 2014 4:30PM - 4:42PM |
J28.00011: The dynamical Casimir effect generates entanglement Simone Felicetti, Mikel Sanz, Lucas Lamata, Guillermo Romero, G\"oran Johansson, Per Delsing, Enrique Solano The existence of vacuum fluctuations, i.e., the presence of virtual particles in empty space, represents one of the most distinctive results of quantum mechanics. It is also known, under the name of dynamical Casimir effect, that fast-oscillating boundary conditions can generate real excitations out of the vacuum fluctuations. Long-awaited, the first experimental demonstration of this phenomenon has been realized only recently, in the framework of superconducting circuits [C. M. Wilson \textit{et al.} Nature 479, 376-379 (2011)]. In this contribution, we will discuss novel theoretical results, showing that the dynamical Casimir effect can be exploited to generate bipartite and multipartite entanglement among qubits. We will also present a superconducting circuit design which can feasibly implement the model considered with current technology. Our scheme is composed of a SQUID device side-coupled to two transmission line resonators, each one interacting with a superconducting qubit. Such proposal can be straightforwardly generalized to the multipartite case, and it can be scaled up to build strongly correlated cavity lattices for quantum simulation and quantum computation. [Preview Abstract] |
Tuesday, March 4, 2014 4:42PM - 4:54PM |
J28.00012: ABSTRACT WITHDRAWN |
Tuesday, March 4, 2014 4:54PM - 5:06PM |
J28.00013: Observation of Autler-Townes effect in a dispersively dressed Jaynes-Cummings System B. Suri, Z.K. Keane, R. Ruskov, Lev S. Bishop, C. Tahan, S. Novikov, J.E. Robinson, F.C. Wellstood, B.S. Palmer We report on the spectrum of a superconducting Al/AlOx/Al transmon qubit coupled to a planar superconducting resonator in the strong dispersive limit. We resolve discrete peaks in the transition spectrum, each corresponding to a different number of photons. At a base temperature of 30 mK and in the absence of a coherent drive on the resonator, we find a weak n = 1 photon peak along with the n = 0 photon peak in the qubit spectrum, corresponding to a population of 5.474 GHz photons at an effective resonator temperature of T = 120mK. Two-tone spectroscopy using independent coupler and probe tones reveals an Autler-Townes splitting in the thermal n = 1 photon peak. The observed effect is explained accurately using the four lowest levels of the dispersively dressed qubit-resonator system and compared to results from numerical simulations of the steady-state master equation for the coupled system. [Preview Abstract] |
Tuesday, March 4, 2014 5:06PM - 5:18PM |
J28.00014: Towards Electromagnetically Induced Transparency in a Transmon Sergey Novikov, J.E. Robinson, Z.K. Keane, B. Suri, F.C. Wellstood, B.S. Palmer We have observed the Autler-Townes (AT) doublet in a superconducting Al/AlO$_{\mbox{x}}$/Al transmon qubit that acts as an artificial atom embedded in a three-dimensional Cu microwave cavity at a temperature of 22 mK.\footnote{S. Novikov \textit{et al.}, Phys. Rev. B 88, 060503(R) (2013).} The long coherence time ($\sim$40 $\mu$s) of the transmon enables us to observe a clear AT splitting, such that three-level density matrix simulations with no free parameters provide excellent fits to the data. Due to specifics of inter-level transition rates in the transmon, the regime of electromagnetically induced transparency (EIT) was not achievable. We will discuss our progress towards engineering the decay rates of the system with the goal of crossing over from the AT to EIT regime. [Preview Abstract] |
Tuesday, March 4, 2014 5:18PM - 5:30PM |
J28.00015: A Quantum Simulation on the Emergence of Lorentz Invariance David Zueco, Fernando Quijandr\'Ia, Diego Blas, Oriol Puj\`olas Lorentz invariance (LI) is one of the best tested symmetries of Nature. It is natural to think that LI is a fundamental property. However, this does not need to be so. In fact, it could be an emergent symmetry in the low energy world. One motivation on Lorentz-violating theories may come from consistent non-relativistic models of gravity, where LI appears at low energies. The basic approach is by taking two interacting quantum fields. The bare (uncoupled fields) have different light velocities, say v1 and v2. The coupling tends to ``synchronize'' those velocities providing a common light velocity: the LI emergence. So far, only perturbative calculations are available. In this perturbative regime the emergence of LI is too slow. Therefore it is mandatory going beyond perturbative calculations. In this talk I will discuss that such models for emergent Lorentz Invariance can be simulated in an analog quantum simulator. In 1+1 dimensions two transmission lines coupled trough Josephson Junctions do the job. We show that the emergence can be checked by measuring photon correlations. Everything within the state of the art in circuit QED. We show that our proposal can provide a definite answer about the LI emergence hypothesis in the strong coupling regime. [Preview Abstract] |
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