Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session Y51: Fluxonium, Flux Qubits, and Novel Superconducting Qubits |
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Sponsoring Units: GQI Chair: William Oliver, MIT Lincoln Laboratory Room: 398 |
Friday, March 17, 2017 11:15AM - 11:27AM |
Y51.00001: A fluxonium-based artificial molecule with a tunable magnetic moment A. Kou, W.C. Smith, U. Vool, R.T. Brierley, H. Meier, L. Frunzio, S.M. Girvin, L.I. Glazman, M.H. Devoret We have designed and measured an engineered artificial molecule, composed of two strongly coupled fluxonium atoms, which possesses a tunable magnetic moment. An externally applied magnetic flux tunes the molecule between two regimes: one in which the ground-excited state manifold has a magnetic dipole moment and one in which the ground-excited state manifold has only a magnetic quadrupole moment. By varying the applied external flux, we find the coherence of the molecule to be limited by local flux noise. [Preview Abstract] |
Friday, March 17, 2017 11:27AM - 11:39AM |
Y51.00002: Coherent dynamics of collective modes in the fluxonium qubit Farshad Foroughi, Etienne Dumur, Doriane Drolet, Yuriy Krupko, Remy Dassonneville, Luca Planat, Javier Puertas-Martinez, Cecile Naud, Olivier Buisson, Nicola Roch, Ioan Pop, Wiebke Guichard When biased at the sweet spot, the fluxonium qubit outperforms any other superconducting qubit regarding the relaxation time T1. This performance is related to the implementation of a superinductor made of a Josephson junction chain. We have fabricated and measured a 3D fluxonium qubit. The relaxation time peaks at half flux quantum at about T1=450$\mu$s. In the standard fluxonium circuit one can neglect the electromagnetic modes of the Josephson junction chain because their frequency is much higher than the qubit frequency. We present on-going results on the design of a fluxonium qubit where the frequencies of these electromagnetic modes is in the order of the qubit frequency. We expect coherent dynamics between the qubit and the collective modes. [Preview Abstract] |
Friday, March 17, 2017 11:39AM - 11:51AM |
Y51.00003: Effective \boldmath$\cos n \varphi$ Josephson element W.C. Smith, A. Kou, U. Vool, L. Frunzio, M.H. Devoret |
Friday, March 17, 2017 11:51AM - 12:03PM |
Y51.00004: Abstract Withdrawn Lambda systems, with a metastable state in addition to the ground state, naturally occur in many atomic systems. Atomic lambda systems offer many potential applications in quantum information processing, including single photon transistors and quantum memories. In superconducting qubits, ladder type systems are most common. Useful lambda systems have proven elusive. Following [1], we create an effective lambda system formed from the Jaynes-Cummings dressed states of a superconducting qubit-cavity system. Using two-photon driving, the system can be controlled as a conventional lambda system. We characterize the performance of the device and the suitability of it for various applications. \newline \newline [1] J.E. Robinson, S.P. Premaratne, B. Suri, F.C. Wellstood, B.S. Palmer, S. Novikov, T. Sweeney. Raman coherence in a circuit quantum electrodynamics lambda system. \it{Nature Physics}, 12: 75-79, 2016. |
Friday, March 17, 2017 12:03PM - 12:15PM |
Y51.00005: The fluxonium as a lambda system U. Vool, A. Kou, W. C. Smith, K. Serniak, I. M. Pop, S. Shankar, L. Frunzio, S. M. Girvin, M. H. Devoret A lambda system is a 3-level system in which two low-energy states can transition to a third higher-energy state by a coherent drive but not to each other. Lambda systems are commonly implemented in systems relying on atomic transitions. In the field of superconducting quantum circuits, the fluxonium qubit, an artificial atom consisting of a Josephson junction shunted by a super-inductance, is a unique artificial atom with highly non-linear energy levels. At half-flux quantum it has two low-energy states with a long energy lifetime, and so is a perfect candidate for a lambda system. However, selection rules in the fluxonium qubit prohibit transitions between low-energy states and higher-energy states of the same parity - therefore there is no state that both low energy states can couple to. In this talk, we will introduce a method which uses 3-wave coupling to address forbidden transitions between levels of the fluxonium qubit, and present preliminary experimental results. [Preview Abstract] |
Friday, March 17, 2017 12:15PM - 12:27PM |
Y51.00006: Realizing a Heavy Fluxonium Circuit Nate Earnest, Yao Lu, Nicholas Irons, Jay Lawrence, Jens Koch, David Schuster Superconducting qubits are a promising technology for quantum information processing, with several orders of magnitude improvement in coherence times. However, in order to achieve a fault tolerant quantum computer, these times need to be improved. One promising path to enhance lifetimes is to engineer a circuit with suppressed transition matrix elements between the qubit states, making the lifetime robust to environmental sources of decay. While the suppressed transition matrix element improves the lifetime, it also makes state preparation challenging. Here we show that a capacitively shunted fluxonium qubit, a heavy fluxonium, is a promising avenue for realizing a double lambda system: a 4-level system with a double well structure. In this system, transitions between wells (fluxons) is exponentially suppressed by the large effective mass from the increased capacitance, leading to enhanced lifetimes. Meanwhile, transitions within the same well (plasmons) are easily driven and have small dephasing due to their flat band structure, and help couple fluxon transitions. In this talk we will present the experimental results of our heavy fluxonium, addressing measurements of lifetimes/dephasing in different regimes, and exploring different schemes for state preparation and measurement [Preview Abstract] |
Friday, March 17, 2017 12:27PM - 12:39PM |
Y51.00007: Framework for Flux Qubit Design Fei Yan, Archana Kamal, Philip Krantz, Daniel Campbell, David Kim, Jonilyn Yoder, Terry Orlando, Simon Gustavsson, William Oliver A qubit design for higher performance relies on the understanding of how various qubit properties are related to design parameters. We construct a framework for understanding the qubit design in the flux regime. We explore different parameter regimes, looking for features desirable for certain purpose in the context of quantum computing. [Preview Abstract] |
Friday, March 17, 2017 12:39PM - 12:51PM |
Y51.00008: Capacitively Shunted Flux Qubits for Multi-qubit Architectures Jaseung Ku, Matthew Hutchings, Yebin Liu, B.L.T. Plourde, Jared Hertzberg, Martin Sandberg, Markus Brink, Easwar Magesan, Firat Solgun, Jerry Chow Capacitively shunted flux qubits (CSFQs) are capable of achieving comparable coherence times to transmon qubits in cQED systems. In addition, the relatively large and positive anharmonicity of the CSFQ can be advantageous for high-fidelity single- and two-qubit gate operations and to address the issue of frequency crowding in multi-qubit systems. We present the design and measurement of various configurations of CSFQ aimed at multi-qubit architectures. [Preview Abstract] |
Friday, March 17, 2017 12:51PM - 1:03PM |
Y51.00009: Properties and Gate Control of the 0-Pi Qubit, Part 1: Disorder and Coherence Peter Groszkowski, Agustin Di Paolo, Arne L. Grimsmo, Alexandre Blais, Jens Koch Superconducting circuits are considered one of the most promising architectures for the eventual implementation of quantum information processing devices, and the flexibility they provide has led to many novel qubit designs. One such design, called the 0-Pi qubit [Brooks et al., Phys. Rev. A 87, 52306 (2013)], promises to offer robust protection from spontaneous relaxation and dephasing due to 1/f charge and flux noise. In the case where multiple instances of circuit elements do not have precisely the same characteristic parameters, however, the qubit's degree of freedom couples to a spurious, low-energy harmonic mode, which can lead to new decoherence effects. In this talk we present a theoretical study of the realistic scenario of disorder among circuit element parameters, and discuss the implications of such disorder on the 0-Pi device. We investigate the relevant decoherence channels, identify the limiting one, and present estimates for the resulting coherence times of the 0-Pi qubit in multiple parameter regimes. [Preview Abstract] |
Friday, March 17, 2017 1:03PM - 1:15PM |
Y51.00010: Properties and Gate Control of the 0-Pi Qubit, Part 2: Gate Control Agustin Di Paolo, Arne L. Grimsmo, Peter Groszkowski, Jens Koch, Alexandre Blais Coherence times of superconducting qubits have been improved by more than five orders of magnitude over the last fifteen years. This astonishing rise has been possible thanks to the identification and partial suppression of noise sources, as well as to new qubit designs. Inspired by the idea of topological protection, namely to store quantum information in a nonlocal fashion, the 0-Pi qubit design aims at robust protection from several types of noise. However, this natural protection has the side effect of making single-qubit control difficult. Specifically, exponential suppression of local-operator matrix elements between the computational states renders conventional means of single-qubit gates impractical. In this talk, we show how to overcome this challenge by use of novel gate schemes for the 0-Pi qubit, and predict achievable gate fidelities. [Preview Abstract] |
Friday, March 17, 2017 1:15PM - 1:27PM |
Y51.00011: A voltage-controlled superconducting quantum bus Lucas Casparis, Natalie Pearson, Anders KringhĂ¸j, Thorvald Larsen, Ferdinand Kuemmeth, Peter Krogstrup, Jesper Nygard, Karl Petersson, Charles Marcus Superconducting qubits couple strongly to microwave photons and can therefore be coupled over long distances through a superconducting cavity acting as a quantum bus. To avoid frequency-crowding it is desirable to turn qubit coupling off while rearranging qubit frequencies. Here, we present experiments with two gatemon qubits coupled through a cavity, which can be tuned by a voltage-controlled superconducting switch. We characterize the bus tunability and demonstrate switchable qubit coupling with an on/off ratio up to 8. We find that pulsing the bus switch on nanosecond timescales results in the apparent loss of qubit coherence. Further work is needed to understand how dynamic control of the tuneable bus affects qubit operation. [Preview Abstract] |
Friday, March 17, 2017 1:27PM - 1:39PM |
Y51.00012: A magnetic field compatible graphene transmon James G. Kroll, Willemijn Uilhoorn, Damaz de Jong, Francesco Borsoi, Kian van der Enden, Srijit Goswami, Maja Cassidy, Leo. P Kouwenhoven Hybrid circuit QED is a key tool for readout and scaling of both semiconductor-based spin and topological quantum computing schemes. However, traditional approaches to circuit QED are incompatible with the strong external magnetic fields required for these qubits. Here we present measurements of a hybrid graphene-based transmon operating at 1 T. The device consists of coplanar waveguide resonators where the NbTiN thin film is patterned with a dense anti-dot lattice to trap Abriskov vortices, resulting in internal quality factors Qi \textgreater 10\textasciicircum 5 up to 6 T. Furthermore, the atomically thin nature of graphene in combination with the high critical field of its superconducting contacts makes it an ideal system for tolerating strong parallel magnetic fields. We combine these circuit elements to realize a magnetic field compatible transmon qubit. An external gate allows us to change the Josephson energy, and study the corresponding change in the resonator-qubit interaction in the dispersive regime. Two tone spectroscopy reveals a gate-tunable qubit peak at 1T. These experiments open up the possibility of fast charge parity measurements in high magnetic fields for readout of Majorana qubits.. [Preview Abstract] |
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