Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F33: Superconducting Qubits: Novel DesignsFocus
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Sponsoring Units: DQI Chair: Vladimir Manucharyan, University of Maryland, College Park Room: LACC 408B |
Tuesday, March 6, 2018 11:15AM - 11:51AM |
F33.00001: Evolution of Nanowire Transmons and Their Quantum Coherence in Magnetic Field Invited Speaker: Florian Luthi Extending the range of application of circuit QED to magnetic fields of order 0.5 T promises interesting applications, including the control and readout of Majorana systems and the coupling to electron-spin systems. In this talk, we present an experimental study of nanowire transmon qubits with state-of-the-art relaxation and dephasing times exceeding 10 μs at zero magnetic field. We investigate the evolution of transmon transition frequencies, anharmonicity, and coherence up 70 mT, limited by the closing of the superconducting gap induced in the InAs nanowire by the thick, epitaxially contacting Al shell. We investigate various sources contributing to the decoherence. In particular, we find that, unlike in conventional transmons, on-chip charge noise coupling to the Josephson energy plays a dominant role in qubit dephasing. This noise takes the form of strongly-coupled two-level systems switching on 100 ms timescale and a more weakly coupled background producing 1/f noise. We conclude with an update on ongoing efforts to extend operation to 0.5 T using nanowires contacted with thinner, partially covering Al shells. |
Tuesday, March 6, 2018 11:51AM - 12:03PM |
F33.00002: Improving control and coherence of the 0-π qubit Agustín Di Paolo, Peter Groszkowski, Arne Grimsmo, Andras Gyenis, Andrew Houck, Jens Koch, Alexandre Blais Despite the great success of the transmon qubit, progress in the coherence times of this qubit has slowed in recent years. Moreover, research within a given qubit design often leads to incremental improvements, while new qubit proposals have the potential to advance the state-of-the-art on performance metrics more substantially. An example of such a proposal is the recently introduced 0-π qubit [1]. We have already shown that the noise resilience of this device can be superior to that of the transmon [2]. In this talk, we characterize control strategies for the 0-π qubit and present a new way to enhance its coherence, taking into consideration disorder in system parameters. |
Tuesday, March 6, 2018 12:03PM - 12:15PM |
F33.00003: A fully programmable three-qubit superconducting processor with all-to-all longitudinal coupling Tanay Roy, Suman Kundu, Sumeru Hazra, Madhavi Chand, A Bhattacharjee, K Salunkhe, Meghan Patankar, Kedar Damle, Rajamani Vijayaraghavan We recently introduced the “trimon”, a longitudinally coupled three-qubit system based on a multi-mode superconducting circuit. Single-pulse implementation of the Toffoli gate and all-to-all coupling enables universal programmability of the processor. We will first describe how we can reconstruct the density matrix for a three-qubit state using a joint readout scheme. We will then discuss the performance of the elementary controlled-controlled-NOT (CCNOT) gate and the preparation of high-fidelity, two- and three-qubit entangled states. Another unique feature of this system is the ability to implement error-free CCZ gate which simplifies construction of various quantum oracles. We will demonstrate these capabilities by executing various quantum algorithms like Deutsch-Jozsa, Bernstein-Vazirani, Grover, period-finding etc. Finally, we will discuss the possibility of building larger quantum processors using the trimon as a building block. |
Tuesday, March 6, 2018 12:15PM - 12:27PM |
F33.00004: Longitudinally Coupled Three-Qubit Circuits as Building Blocks for a Quantum Processor Sumeru Hazra, Suman Kundu, Tanay Roy, Madhavi Chand, K Salunkhe, Meghan Patankar, Rajamani Vijayaraghavan Efficient implementation of quantum algorithms requires precise control over single and multi-qubit gates in addition to maximum inter-qubit connectivity. We recently demonstrated a new three-qubit device called trimon [1], with all-to-all longitudinal coupling. Trimon has an eight-dimensional Hilbert space which can be controlled with high fidelity by manipulating twelve transitions. A π pulse on any of these transitions implements a generalized Toffoli gate which makes this processor fully programmable. We propose to use the trimon device as the building block for a quantum processor. As a first step, we will present preliminary experimental data demonstrating the conventional cross-resonance gate [2] between a trimon and a transmon. We will conclude by discussing the implementation of inter-trimon gates to realize a 3N-qubit quantum processor. |
Tuesday, March 6, 2018 12:27PM - 12:39PM |
F33.00005: Millimeter-wave interconnects for superconducting quantum devices Marek Pechal, Amir Safavi-Naeini Building extended networks of microwave quantum devices requires efficient coherent links. Current efforts to realize these focus on direct microwave connections by waveguides or cables or on conversion to optical signals and connection by optical fibers. The first approach suffers from losses in the link and requires cooling to millikelvin temperatures. The second needs efficient electrooptical converters which are currently believed to require significant optical pumping powers that impede their operation in cryogenic setups. Here we propose and theoretically analyze an interconnect architecture based on conversion to mm-waves in the 100-1000 GHz range. We study a conversion process based on frequency mixing in nonlinear kinetic inductors and show that its operation requires 9 orders of magnitude less energy per converted qubit than optical conversion. Furthermore, due to the higher energy of mm-wave photons compared to microwaves, links in this frequency domain could be operated at liquid helium temperatures without much added thermal noise. This makes them an appealing alternative to microwave links in cases where cooling of long waveguides to millikelvin temperatures is infeasible. |
Tuesday, March 6, 2018 12:39PM - 12:51PM |
F33.00006: A Quantum Transistor with Superconducting Qubits Niels Jakob Loft, Lasse Kristensen, Christian Andersen, Nikolaj Zinner We show that four qubits with next-to-neighbor Heisenberg interactions works as a spin transistor, i.e. a system with perfect state transfer or perfect blockade depending on the spin state of the system. We also propose how this system can be implemented with state-of-the-art superconducting qubits. |
Tuesday, March 6, 2018 12:51PM - 1:03PM |
F33.00007: Quickly Tunable Refrigerator for Superconducting Quantum Circuits Kuan Tan, Shumpei Masuda, Jan Goetz, Matti Partanen, Dibyendu Hazra, Eric Hyyppä, Joonas Govenius, Russell Lake, Visa Vesterinen, Leif Grönberg, Juha Hassel, Slavomir Simbierowicz, Marton Gunyho, Aarne Keränen, Jani Tuorila, Tapio Ala-Nissila, Matti Silveri, Hermann Grabert, Mikko Möttönen In the past decade, the research on superconducting quantum circuits has provided a great number of superior microwave components such as superconducting qubits, amplifiers, and sensors. Especially in the opertation of qubits, it is of utmost importance to be able to quickly remove any unwanted qubit excitations on demand for fast and accurate initialization. Furthermore, a reduction of excess photon population in qubit-coupled resonators is important in tackling shot-noise-induced dephasing. To this end, we recently introduced a device referred to as a quantum-circuit rerigerator [K. Y. Tan, et al., Nat. Commun. 8, 15189 (2017)]. It is a stand-alone component that can be integrated with most superconducting quantum electric devices without major compromises in their other design criteria. In our experiments, we show how we can tune the dissipation of a superconducting resonator by orders of magnitude just by applying a bias voltage on the refrigerator. The time scale for switching the dissipation on and off is in the nanosecond range. We also observe a tunable Lamb shift owing to the dissipation induced by the refrigirator. |
Tuesday, March 6, 2018 1:03PM - 1:15PM |
F33.00008: Superconducting gatemon qubit based on a proximitized two-dimensional electron gas Lucas Casparis, Malcolm Connolly, Morten Kjaergaard, Natalie Pearson, Anders Kringhøj, Thorvald Larsen, Ferdinand Kuemmeth, Tiantian Wang, Sergei Gronin, Geoffrey Gardner, Michael Manfra, Charles Marcus, Karl Petersson The nonlinear inductance generated by Josephson junctions (JJs) is used extensively in quantum information processors based on superconducting circuits. The inductance is either fixed by the metal-oxide dimensions of a single JJ, or magnetically tuned using a superconducting quantum interference device with current-biased flux lines. One tantalizing all-electric alternative are superconductor-semiconductor hybrid JJs with gate-tuneable critical currents. Gatemons have demonstrated the feasibility of this approach using nanowire JJs to control superconducting qubits in the transmon regime [1, 2]. Here we demonstrate that semiconducting channels etched from a wafer-scale two-dimensional electron gas (2DEG) are a natural platform for building a truly scalable gatemon-based universal quantum computer. We show 2DEG gatemons meet the requirements by performing arbitrary voltage-controlled rotations around the Bloch sphere and two-qubit swap operations. We measure qubit lifetimes up to ~2 us, limited by dielectric loss in the 2DEG host substrate. |
Tuesday, March 6, 2018 1:15PM - 1:27PM |
F33.00009: In-situ tunable environment for superconducting qubits Jan Goetz, Matti Silveri, Kuan Tan, Matti Partanen, Marton Gunyho, Dibyendu Hazra, Visa Vesterinen, Juha Hassel, Leif Grönberg, Hermann Grabert, Mikko Möttönen Superconducting quantum circuits hold great potential in providing revolutionizing practical applications such as quantum sensing or computing. However, in many cases noise limits the operation and the fidelity of these circuits. Here we introduce a concept that exploits noise instead of trying to reduce it. Our concept uses photon-assisted single-electron tunneling as a controlled source for dissipation in superconducting qubits. We show how the recently developed quantum-circuit refrigerator [1], QCR, is suitable to control the dynamics of superconducting qubits. In our experiments, the QCR works as a voltage-controlled environmental bath for the qubit. The qubit-bath coupling strength can be tuned over several orders of magnitude on a nanosecond timescale. Such a tunable environment is promising for fast qubit reset and studies of dissipative open quantum circuits. Our highly integrable circuit architecture may prove useful in the initialization of qubit arrays and in dissipation-assisted quantum annealing. |
Tuesday, March 6, 2018 1:27PM - 1:39PM |
F33.00010: Development of Superconducting Qubit Circuits to Coherently Probe Majorana Zero Modes Part I: Device Theory and Design Anders Kringhøj, Willemijn Uilhoorn, Lucas Casparis, James Kroll, Thorvald Larsen, Bernard Van Heck, Tim Stegwee, Robert McNeil, Marina Hesselberg, Oscar Erlandsson, Jesper Nygard, Peter Krogstrup, Gijs De Lange, Karl Petersson, Leo Kouwenhoven, Charles Marcus A proximitized semiconducting nanowire (NW) with high spin-orbit coupling is one of the most promising candidate systems to achieve a topologically protected qubit. Several proposals for achieving such a qubit use proximitized superconducting islands connected via gate-tunable Josephson junctions [1,2]. When two such islands are tuned to the topologically regime the hybridization of the Majorana zero modes at the junction give rise to the fractional Josephson coupling. This additional coupling shows as additional features in the transition spectrum. |
Tuesday, March 6, 2018 1:39PM - 1:51PM |
F33.00011: Development of Superconducting Qubit Circuits to Coherently Probe Majorana Zero Modes Part II: Experimental Results Willemijntje Uilhoorn, Anders Kringhøj, James Kroll, Lucas Casparis, Thorvald Larsen, Bernard Van Heck, Tim Stegwee, Robert McNeil, Marina Hesselberg, Oscar Erlandsson, Jesper Nygard, Peter Krogstrup, Karl Petersson, Gijs de Lange, Charles Marcus, Leo Kouwenhoven A proximitized semiconducting nanowire (NW) with high spin-orbit coupling is one of the most promising candidate systems to achieve a topologically protected qubit. Several proposals for achieving such a qubit use proximitized superconducting islands connected via gate-tunable Josephson junctions [1,2]. When two such islands are tuned to the topological regime the hybridization of the Majorana zero modes at the junction give rise to the fractional Josephson coupling. This additional coupling shows as additional features in the transition spectrum. |
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