Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session T39: Focus Session: Quantum Foundations Studies with Superconducting Qubits |
Hide Abstracts |
Sponsoring Units: GQI Chair: Alexander Korotkov, University of California, Riverside Room: 213AB |
Thursday, March 5, 2015 11:15AM - 11:51AM |
T39.00001: Continuous measurement of two spatially separated superconducting qubits: quantum trajectories and statistics Invited Speaker: Nicolas Roch Measurement can be harnessed to probabilistically generate entanglement in the absence of local interactions, for example between spatially separated quantum objects. Continuous weak measurement allows us to observe the dynamics associated with this process. In particular, we perform joint dispersive readout of two superconducting transmon qubits separated by one meter of coaxial cable. We track the evolution of a joint quantum state under the influence of measurement, both as an ensemble and as a set of individual quantum trajectories. Analyzing the statistics of such quantum trajectories can shed new light on the underlying entangling mechanism. [Preview Abstract] |
Thursday, March 5, 2015 11:51AM - 12:27PM |
T39.00002: Quantum Measurement in Superconducting Circuits Invited Speaker: Kater Murch In recent years, there has been immense progress in the ability to control and measure superconducting circuits. These abilities have enabled several different experiments that address the fundamental physics of quantum measurement, ranging from the observation of non-classical weak values, to the generation of entanglement through measurement and the tracking of individual quantum trajectories. I will review recent progress in the field and discuss how these advances add to the foundations of quantum mechanics. [Preview Abstract] |
Thursday, March 5, 2015 12:27PM - 12:39PM |
T39.00003: Steady-state entanglement of spatially separated qubits via quantum bath engineering Camille Aron, Manas Kulkarni, Hakan Tureci We propose a scheme for driving a dimer of spatially separated qubits into a maximally entangled non-equilibrium steady state. A photon-mediated retarded interaction between the qubits is realized by coupling them to two tunnel-coupled leaky cavities where each cavity is driven by a coherent microwave tone. The proposed cooling mechanism relies on striking the right balance between the unitary and driven-dissipative dynamics of the qubit subsystem. We map the dimer to an effective transverse-field $XY$ model coupled to a non-equilibrium bath that can be suitably engineered through the choice of drive frequencies and amplitudes. We show that both singlet and triplet states can be obtained with remarkable fidelities. The proposed protocol can be implemented with a superconducting circuit architecture that was recently experimentally realized and paves the way to achieving large-scale entangled systems that are arbitrarily long lived. [Preview Abstract] |
Thursday, March 5, 2015 12:39PM - 12:51PM |
T39.00004: Experimental violation of a Bell-Leggett-Garg inequality using weak measurements, Part I: Avoiding loopholes J. Dressel, T. White, J. Mutus, R. Barends, A. Megrant, E. Jeffrey, D. Sank, J. Kelly, B. Campbell, Y. Chen, Z. Chen, B. Chiaro, A. Dunsworth, I.-C. Hoi, C. Neill, P.J.J. O'Malley, P. Roushan, C. Quintana, A. Vainsencher, J. Wenner, A. Fowler, A.N. Korotkov, A.N. Cleland, J.M. Martinis We demonstrate the violation of a hybrid Bell-Leggett-Garg inequality that avoids both the disjoint sampling and fair sampling loopholes that are common to traditional Bell inequalities. Our algorithm uses sequential weak measurements of a Bell state that are implemented with four superconducting Xmon qubits. In this first of two talks, we detail the high-fidelity partial projections that are needed for this violation, which are realized by entangling an ancilla qubit to each data qubit using a controlled-Z two-qubit gate. After calibration of the ancilla readout, these partial projections indirectly measure qubit expectation values with a tunable amount of state disturbance. For sufficiently weak disturbance, the inequality can be violated using all the data collected in a single configuration. [Preview Abstract] |
Thursday, March 5, 2015 12:51PM - 1:03PM |
T39.00005: Experimental violation of a Bell-Leggett-Garg inequality using weak measurements, Part II: The Violation T.C. White, J. Mutus, J. Dressel, J. Kelly, R. Barends, A. Megrant, E. Jeffrey, D. Sank, B. Campbell, Y. Chen, Z. Chen, B. Chiaro, A. Dunsworth, A. Fowler, I.-C. Hoi, C. Neill, P.J.J. O'Malley, P. Roushan, C. Quintana, A. Vainsencher, J. Wenner, A.N. Korotkov, A.N. Cleland, J.M. Martinis We experimentally demonstrate the violation of a hybrid Bell-Leggett-Garg inequality that avoids both the disjoint sampling and fair sampling loopholes that are common to traditional Bell inequalities. Our algorithm uses sequential weak measurements of a Bell state that are implemented with four superconducting Xmon qubits. In this second of two talks, we present experimental detail on the measurement of the CHSH correlator and the analysis of error mechanisms. We find that the dependence of the correlations on the measurement strength shows excellent agreement with theoretical predictions, but the magnitude of the correlator varies greatly with system fidelity. For sufficiently weak and high fidelity measurements, we achieve a violation that is many standard deviations above the classical limit. [Preview Abstract] |
Thursday, March 5, 2015 1:03PM - 1:15PM |
T39.00006: Pre- and post-selected averaging of continuous weak measurement of a superconducting qubit Neda Forouzani, Dian Tan, Kater Murch A superconducting qubit undergoing driven unitary evolution is continuously monitored to observe the time evolution of its quantum state. The continuous measurement signals are dominated by noise, but averaging many measurement signals can reveal information about the ensemble evolution. We use a projective measurement to herald an initial state. The average of many measurements conditioned on the herald yields damped Rabi oscillations. However, if we average the measurement signals conditioned on a final projective measurement, we observe Rabi oscillations that grow in amplitude to approach the final state. These oscillations are the time reverse of the average that is conditioned on the initial state. We can also use the measurement signal to track the individual quantum trajectories of the qubit as it evolves in competition between measurement dynamics and the unitary drive. We use these trajectories to examine the time symmetry of the pre- and post-selected averaged signals. [Preview Abstract] |
Thursday, March 5, 2015 1:15PM - 1:27PM |
T39.00007: Prediction and retrodiction for a continuously monitored superconducting qubit Dian Tan, Kater Murch, Steven Weber, Irfan Siddiqi, Klaus Moelmer We use weak measurement to track single trajectories of a superconducting qubit embedded in a three-dimensional cavity which is subjected to continuous monitoring and driven unitary evolution. The information inferred from the measurement record is incorporated in a density matrix $\rho_{t}$, which is conditioned on probe results until $t$, and in an auxiliary matrix $E_{t}$, which is conditioned on probe results obtained after $t$. We employ a stochastic master equation to propagate $\rho_{t}$ forward in time to make predictions about weak and strong qubit measurements performed at time $t$. After these measurements, the system is subject to further probing and unitary evolution, and we propagate $E_{t}$ backward in time to make retrodictions about past measurements. Our experiments show that the predictions conditioned on $\rho$ and $E$ are more confident and nontrivially different than the predictions based only on $\rho$. [Preview Abstract] |
Thursday, March 5, 2015 1:27PM - 1:39PM |
T39.00008: Violating the Modified Helstrom Bound with Nonprojective Measurements Alexander N. Korotkov, Justin Dressel, Todd A. Brun For the task of discriminating two pure states of a qubit, we provide a rigorous bound for how much projective measurements can minimize a general cost that penalizes both incorrect and declined guesses. This cost bound interpolates between the two-outcome projective strategy of the usual Helstrom bound and the three-outcome unambiguous discrimination strategy. Nonprojective measurements can violate this cost bound to show a clear cost improvement over projective measurements. In the presence of realistic experimental noise, the cost advantage of unambiguous state discrimination is completely destroyed; however, other cost bound violations are more robust, and thus could be experimentally tested with modern superconducting qubit implementations. [Preview Abstract] |
Thursday, March 5, 2015 1:39PM - 1:51PM |
T39.00009: Casimir-Polder-like Effect in a Superconducting Circuit System Peter Groszkowski, Eduardo Martin-Martinez, Chris Wilson, Frank Wilhelm Casimir-type forces arise when the ground state energy of a quantum field depends on a classically-treated degree of freedom. The first example of such forces was proposed by Casimir, when he considered the attractive force that arises between two neutral, conducting plates placed in a vacuum. In this talk, we will discuss a variation of the Casimir-Polder effect, the force between an atom and a conducting plate, in a superconducting circuit consisting of a tunable cavity coupled to a qubit. We will describe an analogous ``Casimir force'' on the cavity's effective boundary condition, outline the consequences of longitudinal versus transverse coupling between the qubit and cavity, and discuss the relevance of the field self-interaction term ($A^{2}$). Finally, we will briefly touch on prospects related to measurement. [Preview Abstract] |
Thursday, March 5, 2015 1:51PM - 2:03PM |
T39.00010: Vacuum-Induced Berry Phase Measured Via a Phase-Tunable Atom-Field Interaction S. Gasparinetti, S. Berger, A. A. Abdumalikov, M. Pechal, S. Filipp, A. Wallraff Geometric phases incorporate a fundamental aspect of quantum mechanics. They are at the heart of many quantum phenomena in solid-state physics, from the quantum Hall effect to topologically protected phases, and may provide a resource for quantum computation. We present the first experimental observation of the vacuum-induced Berry phase [1], a geometric effect that arises when the phase of a quantized field mode coupled to an atom is adiabatically steered. Our atom-field system is a transmon embedded in a 3D microwave cavity. A phase-coherent microwave tone induces a tunable interaction between the third level of the transmon and a long-lived mode of the cavity [2]. By adiabatically steering the phase of the interaction, we demonstrate that the qubit accumulates a geometric phase even when the cavity mode is empty. We characterize this effect by varying the effective atom-field detuning as well as the photon number in the cavity mode. \newline [1] I.~Fuentes-Guridi, A.~Carollo, S.~Bose, and V.~Vedral, Phys.~Rev.~Lett.~\textbf{89}, 220404 (2002). \newline [2] M.~Pechal, L.~Huthmacher, C.~Eichler, S.~Zeytino\v{g}lu, A.~A.~Abdumalikov, S.~Berger, A.~Wallraff, and S.~Filipp, Phys.~Rev.~X \textbf{4}, 041010 (2014). [Preview Abstract] |
Thursday, March 5, 2015 2:03PM - 2:15PM |
T39.00011: ABSTRACT WITHDRAWN |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700