Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session H28: Qubit Readout and Open SystemsFocus

Hide Abstracts 
Sponsoring Units: DQI Chair: Archana Kamal Room: BCEC 161 
Tuesday, March 5, 2019 2:30PM  3:06PM 
H28.00001: Nonequilibrium thermodynamics and manybody dynamics in open quantum systems Invited Speaker: Masahito Ueda Quantum gas microscopy has revolutionarized our view on quantum manybody systems where atoms trapped in an optical lattice can be observed in real time at the singleparticle level. At such extreme precision, the measurement backaction due to Heisenberg's uncertainty relation can no longer be ignored. One should naturally led to the question of whether or not nonequilibrium thermodynamics and statistical physics should be modified be modified and, if so, in what way and, in particular, how thermalization proceeds under continuous observation. A similar situation has emerged in a system of superconducting qubits under feedback control. I will address these issues and closely related problems of thermalization, heating and manybody localization in isolated and open quantum systems. 
Tuesday, March 5, 2019 3:06PM  3:18PM 
H28.00002: Multiplexed Readout of Superconducting Qubits in 3D cQED Architecture Using Impedance Engineered Broadband JPA Suman Kundu, Nicolas Gheeraert, Sumeru Hazra, Tanay Roy, Kishor Salunkhe, Meghan P. Patankar, Rajamani Vijayaraghavan We propose and demonstrate a frequencymultiplexed readout scheme in 3D cQED architecture. We use four transmon qubits coupled to individual rectangular cavities which are aperturecoupled to a single rectangular waveguide feedline. A coaxial to waveguide transformer at the other end of the feedline allows to launch and collect the multiplexed signal. The reflected readout signal is amplified by an impedance engineered broadband parametric amplifier with 380 MHz of bandwidth. This provides us high fidelity singleshot readout of multiple qubits using compact microwave circuitry, an efficient way for scaling up to more qubits in 3D cQED. We also discuss possible designs for multiplexing larger number of qubits. Finally, we discuss the saturation properties of our broadband JPA and explore a few approaches to improve them to increase the number of qubits that can be measured simultaneously. 
Tuesday, March 5, 2019 3:18PM  3:30PM 
H28.00003: Increasing qubit readout fidelity and efficiency with twomode squeezed light Xi Cao, Gangqiang Liu, TzuChiao Chien, Pinlei Lu, Michael Hatridge Implementing quantum information processing on a large scale with flawed components requires highly efficient, quantum nondemolition (QND) qubit readout. In superconducting circuits, qubit readout using coherent light with fidelity above 99% has been achieved by using a quantumlimited parametric amplifier such as the Josephson Parametric Converter (JPC), as the first stage amplifier. However, further improvement of such measurement is fundamentally limited by the vacuum fluctuations on the ports of the JPC. Alternatively, readout with squeezed input can entangle the vacuum fluctuations in different modes, thus allowing for the reduction of the noise by controlling their interference. In this talk, we demonstrate a dispersive qubit readout scheme which exploits the twomode squeezed light generated by a first JPC and processed by a second JPC to form an amplified interferometer [1]. We have observed a 22% improvement in the voltage SignaltoNoise Ratio (SNR) of the measurement compared to coherent light. We can also extend this scheme to generate remote entanglement. We will discuss how the role of losses changes in this system for coherent vs twomode squeezed light. 
Tuesday, March 5, 2019 3:30PM  3:42PM 
H28.00004: crossresonancebased readout scheme of a superconducting flux qubit Fumiki Yoshihara, Sahel Ashhab, Tomoko Fuse, Kouichi Semba We propose a crossresonancebased readout scheme of a superconducting flux qubit, in which a flux qubit is coupled to a resonator, and a microwave flux pulse tuned to the resonator is applied to the flux qubit. At the optimal flux bias, the persistent current of the flux qubit is an increasing or decreasing function of the flux bias, depending on the state of the qubit. When a microwave flux drive is applied to the qubit, the phase of the induced microwave signal felt by the resonator depends on the state of the qubit, and the difference between the two values is 180 degrees. Since this qubitstatedependent phase difference is larger than that of dispersiveinteraction schemes [1], the proposed crossresonancebased readout scheme has the potential to be faster. The proposed scheme takes advantage of the large contrast of the fluxbias dependence of the persistent current, and, hence, faster readout is expected compared to the alternative readout schemes [2, 3], which are mainly for transmon qubits. 
Tuesday, March 5, 2019 3:42PM  3:54PM 
H28.00005: Continuous joint measurement of twoqubit fluorescence: quantum dynamics and entanglement Philippe Lewalle, Andrew N Jordan We consider a continuous weak measurement scheme in which two qubitcavity systems are allowed to fluoresce, and their fluorescence signals are mixed before being routed to a measurement apparatus. We theoretically investigate the stochastic quantum trajectories, qubit state dynamics, and entanglement dynamics between the qubits under such a jointmeasurement scheme. Equivalent systems should be experimentally realizable with existing circuitQED technologies. 
Tuesday, March 5, 2019 3:54PM  4:06PM 
H28.00006: Highfidelity detection of information encoded in bosonic modes: Part I Christopher Wang, Salvatore Elder, Philip Reinhold, Connor Hann, Kevin S Chou, Brian J Lester, Serge Rosenblum, Christopher J Axline, Luigi Frunzio, Liang Jiang, Robert J Schoelkopf Qubit measurements in a computational basis are a necessary component of quantum computation. Examples include measurement at the end of a quantum algorithm and projective measurements during teleported operations. Although qubit readout suffers from errors, they may be repeated if the readout is quantum nondemolition (QND). In this way, individual imperfect readouts can be combined via methods such as majority voting to form a more accurate measurement. The measurement fidelity will be limited, however, by state transitions between qubit basis states. For twolevel qubits, a single relaxation event destroys the information in the qubit. An increased distance in the Hilbert space between basis states for qubits encoded in bosonic modes, however, exponentially suppresses this infidelity limit due to transitions. In this talk, we present a measurement scheme in the circuit quantum electrodynamics (cQED) platform that utilizes repeated QND readouts to suppress measurement infidelity due to both individual readout errors and relaxation. [1] We characterize the fidelity of this scheme in terms of experimental parameters for various encodings. 
Tuesday, March 5, 2019 4:06PM  4:18PM 
H28.00007: Highfidelity detection of information encoded in bosonic modes: Part II Salvatore Elder, Christopher Wang, Philip Reinhold, Connor Hann, Kevin S Chou, Brian J Lester, Serge Rosenblum, Christopher J Axline, Luigi Frunzio, Liang Jiang, Robert J Schoelkopf Singleshot qubit measurement is vital for universal quantum computation. In the field of superconducting qubits, much progress has been made in the readout and amplification chain; nonetheless, stateoftheart measurement fidelities are limited by relaxation and detector inefficiency to about 99%. We present an experimental demonstration of a recent proposal [Hann et al, Phys. Rev. A 98, 022305] to improve measurement fidelities by orders of magnitude. By combining repeated QND measurements with errortolerant encodings, we suppress the effects of both relaxation and detector inefficiency. The results are compared with theoretical predictions and achievable limits are described. 
Tuesday, March 5, 2019 4:18PM  4:30PM 
H28.00008: Design of a Cryogenic, Digital Measurement Circuit for Superconducting Qubits Caleb Howington, Alexander Opremcak, Alex Kirichenko, Oleg Mukhanov, Robert F McDermott, Britton L Plourde As superconducting quantum processors increase in size and complexity, the scalability of standard techniques for qubit control and readout becomes a limiting factor. One vision for a scalable architecture leverages cryogenic, classical control and readout circuitry based on the SFQ (Single Flux Quantum) logic family. Conventional heterodyne readout uses a quantumlimited cryogenic amplifier chain and requires bulky microwave components with multiple rf lines and pump signals, with the result accessible in software at room temperature. An alternative method involves mapping the qubit state onto the photon occupation in a microwave cavity, followed by photon detection using a Josephson Photomultiplier (JPM). The result is stored as a classical circulating current. To convert this current to digital logic, a ballistic Josephson Transmission Line (JTL) can be inductively coupled to the JPM. Fluxons in the JTL are delayed depending on the circulating current in the JPM. A delay detection circuit converts arrival time to a logical 1 or 0. This digital result can then be used by a proximal classical coprocessor performing quantum error detection. Simulations and experimental results with this measurement technique will be discussed. 
Tuesday, March 5, 2019 4:30PM  4:42PM 
H28.00009: Measuring qubit quasiprobability distributions behind outoftimeordered correlators Razieh Mohseninia, Jose Raul Gonzalez Alonso, Mordecai Waegell, Nicole Yunger Halpern, Justin Dressel The nonclassicality of the quasiprobability distribution (QPD) behind an outoftimeordered correlator (OTOC) is a more nuanced witness for information scrambling than the OTOC itself. We use the method introduced in Phys. Rev. A 98, 012132 (2018) to provide different experimental protocols for obtaining such a QPD in a multiqubit system. We show that by strategically averaging sequential measurements of any strength, we can reconstruct both OTOCs and QPDs in spite of disturbances caused by intermediate strong measurements. 
Tuesday, March 5, 2019 4:42PM  4:54PM 
H28.00010: Timeresolved singleshot singlegate RF spin readout in silicon Prasanna Pakkiam, Andrey V. Timofeev, Matthew House, Mark Hogg, Takashi Kobayashi, Matthias Koch, Sven Rogge, Michelle Y Simmons For solidstate spin qubits, singlegate RF readout can minimise the number of gates required for scaleup since the readout sensor can integrate into the existing gates used to manipulate the qubits [1][2]. However, state of the art topological error correction codes benefit from the ability to resolve the qubit state within singleshot, that is, without repeated measurements [3]. Here we show singlegate, singleshot readout of a singlettriplet spin state in silicon, with an average readout fidelity of 82.9% at 3.3kHz measurement bandwidth. We use this technique to measure a triplet T_{} to singlet S_{0} relaxation time of 0.62ms in precision Pdonor quantum dots. We also show that the use of RF readout does not impact the spin lifetimes (S_{0} to T_{} decay remained 2ms at zero detuning). This establishes singlegate sensing as a viable readout method for spin qubits. 
Tuesday, March 5, 2019 4:54PM  5:06PM 
H28.00011: Radiofrequency reflectometry of a quantum dot using an ultralownoise SQUID amplifier Felix Schupp, Natalia Ares, Aquila Mavalankar, Jonathan Griffiths, Geb Jones, Ian Farrer, David A Ritchie, Charles G Smith, George Andrew Davidson Briggs, Edward Laird Faulttolerant spinbased quantum computers will require fast and accurate qubit readout. This can be achieved using radiofrequency reflectometry given sufficient sensitivity to the change in quantum capacitance associated with the qubit states. Here, we demonstrate a 23fold improvement in capacitance sensitivity by supplementing a cryogenic semiconductor amplifier with a SQUID preamplifier. The SQUID amplifier operates at a frequency near 200 MHz and achieves a noise temperature below 550 mK when integrated into a reflectometry circuit, which is within a factor 115 of the quantum limit. It enables a record sensitivity to capacitance of 0.07 aFHz^{0.5} and a sensitivity to oscillating charge of 5.9 x 10^{24}CHz^{0.5}. We use this circuit to measure the stability diagram of a gatedefined quantum dot, and show that the sensitivity should be sufficient for singleshot readout of a singlettriplet qubit in GaAs without a charge sensor. 
Tuesday, March 5, 2019 5:06PM  5:18PM 
H28.00012: Advantages of Independent Heat Sinking of a TwoStage Cryogenic Amplifier for Quantum Dot Readout Joelle Corrigan, Trevor Knapp, John Dodson, Nathan Holman, Brandur Thorgrimsson, Thomas McJunkin, Samuel Neyens, E. R. MacQuarrie, Ryan Foote, Lisa Edge, Susan Coppersmith, Mark Alan Eriksson Reduced device electron temperature while using a cryogenic HEMT amplifier is achieved by moving the amplifier to an adjacent PCB electrically connected to the sample PCB. The amplifier PCB is directly heat sunk to the mixing chamber of a dilution refrigerator, and connects to the sample through a short stainless steel coax. Using straightforward measurements of gain and RMS noise, the two stages are tuned separately to minimize the inputreferred noise for a given level of power dissipation. A single shot measurement with 650 ns rise time using 10 µW of power results in a 2.3:1 SNR and 150mK electron temperature. An electron temperature of 115 mK is achieved with lower power, and the effect of these various powers on SNR is examined for bandwidths of 540kHz and 170kHz. The large amplifier bandwidth enables high frequency lockin measurements, resulting in lower noise data than possible without such an amplifier. The ease of use of cryogenic amplification combined with relatively low electron temperature and large bandwidth provides a useful tool for characterization of semiconductor quantum dot qubits. 
Tuesday, March 5, 2019 5:18PM  5:30PM 
H28.00013: Fast high fidelity qubit readout of a transmon molecule using longitudinal coupling Vladimir Milchakov, Remy Dassonneville, Olivier Buisson, Luca Planat, Sébastien Leger, Javier Puertas, Karthik Srikanth Bharadwaj, Farshad Foroughi, Cecile Naud, Wiebke HaschGuichard, Nicolas Roch The most common technique of qubit readout in cQED relies on the transverse dispersive coupling between a qubit and a microwave cavity. However, despite important progresses, implementing fast high fidelity readout remains a major challenge. Indeed, inferring the qubit state is limited by the tradeoff between speed and accuracy due to Purcell effect and unwanted transitions induced by readout photons in the cavity. To overcome this, we introduce a transmon molecule based on two transmons coupled by a large inductance, which is inserted inside a 3Dcavity. The full system presents one transmon –used as qubit– with a large direct crossKerr(longitudinal) coupling to a nonlinear readout resonator, called polaron mode. This polaron mode results from the hybridization between the microwave cavity and the second mode of the transmon molecule circuit. The direct crossKerr coupling is a key point of our readout scheme since it protects the qubit from Purcell effect. We will present qubit readout performance with fidelity as high as 95.7% in 120ns and discuss the quantum nondemolition properties of this novel readout. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit 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 207403844
(301) 2093200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700