Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session M41: Microwave Quantum Optics & Circuit QED 
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Sponsoring Units: GQI Chair: Evan Jeffrey, Google Inc, Santa Barbara Room: 214A 
Wednesday, March 4, 2015 11:15AM  11:27AM 
M41.00001: Driving with squeezed vacuum in strong dispersive circuitQED Matthew Elliott, Eran Ginossar Recent experiments have demonstrated that it is possible to achieve a significant interaction between a squeezed microwave state and a superconducting qubit. Motivated by the success of coherent driving in circuitQED, we study the dynamics of a twopart system where the squeezed output of a degenerate Josephson parametric amplifier, is used to drive a cavityqubit system. We develop a Gaussian mean field model to describe the cavity state in the strongdispersive regime and use this to investigate its steadystate behaviour. We compare this to full numerical solutions of the master equation, allowing us to also consider transient dynamics. Despite the effect of the qubit nonlinearity, we demonstrate that it is possible to generate a stable, highly squeezed intracavity field in a range of parameters where the qubit can be used to reconstruct the states of the cavity. These results are testable using current experimental setups. Additionally, we discuss possible applications in the characterisation of sources of itinerant squeezed vacuum. [Preview Abstract] 
Wednesday, March 4, 2015 11:27AM  11:39AM 
M41.00002: Measurement of ac Stark shift in a superconducting qubit under strong Rabi drive Yonuk Chong, DongGwang Ha, Jung Hwan Park, Woon Song, Gwan Yeol Park, Soon Gul Lee We present a measurement of ac Stark shift in a superconducting 3D transmon qubit. The qubit is strongly coupled to a superconducting aluminum cavity in circuit QED architecture. We observed the ac Start shift under strong Rabi drive and measured it from detuning behavior of the Rabi oscillations as a function of the Rabi frequency. We also confirmed the shift by the AutlerTownes splitting measurement as a function of the qubit drive power. [Preview Abstract] 
Wednesday, March 4, 2015 11:39AM  11:51AM 
M41.00003: Observation of Dark State in a Threedimensional Transmon Superconducting Qutrit Yuhao Liu, Xinsheng Tan, Dong Lan, Peng Zhao, Jie Zhao, Mengmeng Li, Shudong Huang, Haifeng Yu, Shiliang Zhu, Yang Yu Dark state refers to a particular state of a quantum system that cannot absorb or emit photons in driving fields. It has important applications in quantum information processing and quantum metrology. Here we report the observation of dark state in a threedimensional transmon superconducting qutrit. The transmon qutrit, which has cascade three energy levels $0\rangle$, $1\rangle$ and $2\rangle$, is embedded in the center of a rectangle waveguide cavity. When two tone microwaves are applied resonantly between $0\rangle$, $1\rangle$ and $1\rangle$, $2\rangle$, the state of the system will evolve in time domain. However, if we initialize the qutrit in the coherent superposition state, it will not change with time for certain driving amplitudes. The observed relationship between the initial state and the amplitudes of the two tone microwaves agrees well with the results from numerical calculations. [Preview Abstract] 
Wednesday, March 4, 2015 11:51AM  12:03PM 
M41.00004: Resonance Fluorescence and Photon Correlations Produced by 110 Qubits in 1D Infinite or SemiInfinite Waveguides YaoLung L. Fang, Harold Baranger We study multiple twolevel systems (2LS) coupled to a 1D waveguide in which one end is open and the other is either open (infinite waveguide) or closed (semiinfinite). Resonance fluorescence and twophoton correlations are presented for weak coherent driving. We show that while for a single 2LS coupled to an infinite waveguide the reflected photons are initially antibunched, for a semiinfinite waveguide they become highly bunched. As the number of 2LS increases (up to 10), rapid oscillations build up in the correlations that persist for a long time. At the same time, incoherently reflected photons are mostly distributed within the photonic band gap when driven resonantly, accompanied by sharp side peaks. Our calculations can be explained using the poles of the Green function in the Markovian regime together with the notion of time delay. Finally, in the nonMarkovian regime we demonstrate that a 2LS in a semiinfinite waveguide can no longer be decoupled by placing it at the node of the photonic field, in sharp contrast to a recent experimental finding in the Markovian regime using superconducting qubits. [Preview Abstract] 
Wednesday, March 4, 2015 12:03PM  12:15PM 
M41.00005: Electromagnetically induced transparency and coherent population trapping with a superconducting artificial atom Sergey Novikov, Timothy M. Sweeney, J.E. Robinson, Baladitya Suri, F.C. Wellstood, B.S. Palmer We embed a superconducting Al/AlO$_{\mbox{x}}$/Al transmon qubit that acts as an artificial atom in a threedimensional copper microwave cavity at a temperature of 22 mK. By addressing the hybridized qubitcavity levels with two microwave drives (probe and coupler), we are able to create a $\Lambda$like system with highly asymmetric decay rates. We observe electromagnetically induced transparency, and use this feature to achieve coherent population trapping (CPT) by creating a superposition state with the two drives whose duration is much longer than any coherence times in the system. After the drives are turned off, the resultant CPT dark state is coherent for $T_{CPT} \approx T_2^* = 7.4\;\mu s$. We estimate the \textit{minimum} fidelity of the dark state achievable in this system to be 60\%. These results present a way of superposition and entanglement generation with CW tones in a superconducting system. [Preview Abstract] 
Wednesday, March 4, 2015 12:15PM  12:27PM 
M41.00006: Electromagnetically Induced Superluminal Light in a 3D Transmon Device Timothy M. Sweeney, Sergey Novikov, Baladitya Suri, Shavindra Premarante, JenHao Yeh, F.C. Wellstood, B.S. Palmer Quantum interference in a three level $\Lambda $type system can result in nonlinear optical effects such as electromagnetically induced transparency/absorption (EIT/EIA), slow, and fast light. We have created a $\Lambda $ system with an effectively metastable state by dispersively coupling an Al/AlOx/Al transmon qubit (T1 $=$4 us) to a 3D Cu microwave cavity (T1$=$340ns). By probing the transmission through the cavity while pumping a qubitcavity sideband yields a large change in the dispersion. We observe group advances of up to 10 us for Gaussian pulses propagating through the system, corresponding to a group index of 176,000. [Preview Abstract] 
Wednesday, March 4, 2015 12:27PM  12:39PM 
M41.00007: A superconducting qubit coupled to propagating acoustic waves Martin V. Gustafsson, Thomas Aref, Anton Frisk Kockum, Maria K. Ekstr\"{o}m, G\"{o}ran Johansson, Per Delsing Mechanical devices in the quantum regime have so far consisted mainly of suspended resonators, where standing modes can be populated with quanta of vibrational energy. We present a fundamentally different system, where the mechanical excitation is not restricted to a specific mode and location. Instead, we demonstrate strong nonclassical coupling between \emph{propagating} phonons and a superconducting qubit.\footnote{Gustafsson \emph{et al.}, Science \textbf{346}, 207 (2014)} The qubit is fabricated on a piezoelectric substrate, and is designed to interact with Surface Acoustic Waves (SAWs) in the gigahertz frequency range. A separate onchip transducer allows us to launch SAWs toward the qubit from a distance and pick up SAW phonons that the qubit reflects and emits. In a series of experiments where the qubit is addressed both electrically and acoustically, we show that the qubit couples much more strongly to SAWs than to any electrical modes. The low speed of sound sets phonons apart from photons as a medium for transporting quantum information, and should enable realtime manipulation of propagating quanta. The short acoustic wavelength and strong piezoelectric coupling should also allows regimes of interaction to be explored which cannot be reached in photonic systems. [Preview Abstract] 
Wednesday, March 4, 2015 12:39PM  12:51PM 
M41.00008: Strong qubitphoton interactions in a superconducting 1D open space Pol FornDiaz, JeanLuc Orgiazzi, Martin Otto, Ali Yurtalan, Borja Peropadre, JuanJose GarciaRipoll, Christopher Wilson, Adrian Lupascu The field of superconducting quantum circuits has seen much progress using many ideas formerly developed for atomic systems, while at the same time exploring new avenues unattainable in other quantum systems. A novel, promising architecture for fundamental studies of quantum electrodynamics in one dimension can be built by coupling a single superconducting qubit to a transmission line [1]. The qubit interacts with the modes of the transmission line, behaving like a single scatterer that can interfere strongly with propagating photons. The interaction between the qubit and the propagating modes of the line can be made ultrastrong, thus enabling a new domain of physics and applications to be investigated. We will present preliminary results on an experiment consisting in a flux qubittransmission line system at different coupling strengths and its connection to existing models of spinboson physics [2]. \\[4pt] [1] Astafiev et al., Science 327, 840 (2010), Hoi et al., PRL 107, 073601 (2011)\\[0pt] [2] Peropadre et al., PRL 111, 243602 (2013) [Preview Abstract] 
Wednesday, March 4, 2015 12:51PM  1:03PM 
M41.00009: Flux qubit ultrastrongly coupled to two resonators A. Baust, E. Hoffmann, M. Haeberlein, M.J. Schwarz, P. Eder, J. Goetz, F. Wulschner, E. Xie, L. Zhong, K. Fedorov, E.P. Menzel, F. Deppe, A. Marx, R. Gross Circuit quantum electrodynamics has not only become a versatile toolbox for quantum information processing, but is also a powerful platform for the investigation of lightmatter interaction. The coupling strength between microwave resonators and qubits acting as artificial atoms can be tuned over several orders of magnitude and can even reach the regime of ultrastrong coupling.We present spectroscopic data of a flux qubit coupled galvanically to the signal lines of two coplanar stripline resonators. We discuss the complex mode spectrum and show that the coupling strength between the qubit and one resonant mode reaches 15\% of the respective mode frequency. Noticably, the high coupling strength is reached solely by the geometric layout of the qubit without utilizing additional coupling elements such as Josephson junctions. Our data exhibit a pronounced BlochSiegert shift and therefore represent an experimental evidence for the breakdown of the JaynesCummings model. This work is supported by the DFG via SFB 631, and EU projects CCQED and PROMISCE. [Preview Abstract] 

M41.00010: ABSTRACT WITHDRAWN 
Wednesday, March 4, 2015 1:15PM  1:27PM 
M41.00011: Circuit QED Photonics David Zueco, Eduardo S\'anchezBurillo, Juanjo Garc\'IaRipoll, Luis Mart\'InMoreno In this talk we report our theoretical results for the scattering of few photons against few two level systems. The photons travel through an open superconducting coplanar waveguide transmission line and the two level systems can be flux qubits or transmons. Several phenomena will be discussed: the linear and nonlinear behavior as a function of the ratio between the number of photons and number of qubits. For the case of flux qubits we discuss the cases of strong and ultrastrong linequbits coupling. Different phenomena are found and described: Fano profiles, Raman scattering, photon generation and novel and nonperturbative qubitqubit interecations through the line. Finally, we consider the case of transmon qubits. We theoretically demonstrate that driven transmons can be used as a minimal setup for doing up and downcoversion. By minimal, we mean that sending just one photon two photons are generated through the qubit. In our calculations, the parameters are taken from the chip reported in a recent Science paper by the Wallraff group [van Loo et al, Science 342, 1494 (2013)] . [Preview Abstract] 
Wednesday, March 4, 2015 1:27PM  1:39PM 
M41.00012: Lightmatter decoupling and $A^2$ term detection in superconducting circuits Juan Jose GarciaRipoll, Borja Peropadre, Simone De Liberato We study the spontaneous emission of a qubit interacting with a onedimensional waveguide through a realistic minimalcoupling interaction. We show that the diamagnetic term $A^2$ leads to an effective decoupling of a single qubit from the electromagnetic field. This effect is observable at any range of qubitphoton couplings. For this we study a setup consisting of a transmon that is suspended over a transmission line. Assuming a standard model of qubitline interaction, we prove that the relative strength of the $A^2$ term is controlled with the qubitline separation and show that, as a consequence, the spontaneous emission rate of the suspended transmon onto the line can increase with such separation, instead of decreasing.\footnote{Lightmatter decoupling and $A^2$ term detection in superconducting circuits, J. J. GarciaRipoll, B. Peropadre, S. De Liberato, arXiv:1410.7785} [Preview Abstract] 
Wednesday, March 4, 2015 1:39PM  1:51PM 
M41.00013: Beyond strong coupling in a massively multimode cavity Neereja Sundaresan, Yanbing Liu, Darius Sadri, Laszlo Szocs, Devin Underwood, Moein Malekakhlagh, Hakan Tureci, Andrew Houck We present experiments in a new regime of cavity quantum electrodynamics (cQED), the multimode strong coupling regime, in which the qubitcavity coupling is comparable to the free spectral range, thus requiring the collective treatment of all modes along with the qubit. Here we show that this regime is accessible in circuit QED by coupling a 90MHz microwave cavity with a transmon qubit, resonant with the 75th harmonic with a coupling strength exceeding 30MHz. When driving this system, we observe multimode fluorescence consistent with cavityenhanced sideband emission, with unexpected multiphoton processes and the emergence of ultranarrow linewidths. This multimode coupling opens the door for a wide range of potential experiments, including studying the manifestation of complex manybody phenomena, the breakdown of the rotating wave approximation, and the bridge between discrete and continuous Hilbert spaces. [Preview Abstract] 
Wednesday, March 4, 2015 1:51PM  2:03PM 
M41.00014: Multifrequency modes in superconducting resonators: Bridging frequency gaps in offresonant couplings Christian Kraglund Andersen, Klaus M{\O}lmer A SQUID inserted in a superconducting waveguide resonator imposes current and voltage boundary conditions that makes it suitable as a tuning element for the resonator modes. If such a SQUID element is subject to a periodically varying magnetic flux, the resonator modes acquire frequency side bands. We calculate the multifrequency eigenmodes and these can couple resonantly to physical systems with different transition frequencies and this makes the resonator an efficient quantum bus for state transfer and coherent quantum operations in hybrid quantum systems. As an example of the application, we determine their coupling to transmon qubits with different frequencies and we present a bichromatic scheme for entanglement and gate operations. In this calculation, we obtain a maximally entangled state with a fidelity $F=95 \%$. Our proposal is competitive with the achievements of other entanglementgates with superconducting devices and it may offer some advantages: (i) There is no need for additional control lines and dephasing associated with the conventional frequency tuning of qubits. (ii) When our qubits are idle, they are far detuned with respect to each other and to the resonator, and hence they are immune to cross talk and Purcellenhanced decay. [Preview Abstract] 
Wednesday, March 4, 2015 2:03PM  2:15PM 
M41.00015: Amplitude Bistability in the Multimode Regime of CircuitQED Moein Malekakhlagh, Neereja Sundaresan, Yanbing Liu, Darius Sadri, Andrew Houck, Hakan Tureci In theory of dynamical systems, bistability refers to a situation where the system has two possible stable equilibrium states. For certain optical devices, it is possible to have two resonant transmission states that only differ in amplitude and is referred as ``optical amplitude bistability.'' This phenomenon occurs due to nonlinear nature of lightmatter interaction where the light absorption or blockade by the absorber strongly depends on the drive strength. The transition between these two bistable solutions happens when the absorber is saturated and no longer capable of blocking light. In this talk, we study the dynamics of a transmon qubit coupled to a large number of modes of a long superconducting resonator and driven by an external microwave drive. We introduce a generalized theory of multimode amplitude bistability first discussed by C.M. Savage and H.J. Carmichael [1] for a resonant single mode cavity. We will demonstrate that bistability is a characteristic of the entire system including the qubit and all modes of the resonator and can be characterized analytically by the knowledge of two collective cooperativity parameters. \\[4pt] [1] IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 24, NO. 8, AUGUST 1988 [Preview Abstract] 
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