Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session M75: Novel Superconducting qubit designs and components IFocus
|
Hide Abstracts |
Sponsoring Units: DQI Chair: Iris Mowgood, Chapman University Room: Room 401/402 |
Wednesday, March 8, 2023 8:00AM - 8:36AM |
M75.00001: Gralmonium: Granular Aluminum Nano-Junction Fluxonium Qubit Invited Speaker: Dennis Rieger Mesoscopic Josephson junctions (JJs), consisting of overlapping superconducting electrodes separated by a nanometer thin oxide layer, provide a precious source of nonlinearity for superconducting quantum circuits and are at the heart of state-of-the-art qubits, such as the transmon and fluxonium. Here, we show that in a fluxonium qubit the role of the JJ can also be played by a lithographically defined, self-structured granular aluminum (grAl) nano-junction: a superconductor-insulator-superconductor (SIS) JJ obtained in a single layer, zero-angle evaporation. The measured spectrum of the resulting qubit, which we nickname gralmonium, is indistinguishable from the one of a standard fluxonium qubit. Remarkably, the lack of a mesoscopic parallel plate capacitor gives rise to an intrinsically large grAl nano-junction charging energy in the range of tens of GHz, comparable to its Josephson energy EJ. We measure average energy relaxation times of T1 = 10 µs and Hahn echo coherence times of T2echo = 9 μs. The exponential sensitivity of the gralmonium to the EJ of the grAl nano-junction provides a highly susceptible detector. Indeed, we observe spontaneous jumps of the value of EJ on timescales from milliseconds to days, which offer a powerful diagnostics tool for microscopic defects in superconducting materials. |
Wednesday, March 8, 2023 8:36AM - 8:48AM |
M75.00002: Implementation of a Josephson Phase Slip Qubit Mallika T Randeria, Steven M Disseler, Cyrus F Hirjibehedin, Thomas M Hazard, Steven J Weber, Rabindra Das, David K Kim, Alexander Melville, Bethany M Niedzielski, Jonilyn L Yoder, Andrew J Kerman Analog quantum simulation is gaining traction as a path to studying relevant many-body quantum interactions. Of the many qubit modalities, flux qubits in superconducting circuits are well suited to simulate the quantum transverse field Ising model. However, this architecture has been limited to modeling Hamiltonians with only a ZZ coupling between qubits. Here we discuss a novel type of superconducting qubit, the Josephson phase slip qubit (JPSQ), a vector spin-1/2 system designed to achieve the static emulation of the full Heisenberg Hamiltonian. We present our implementation of a JPSQ and characterize its tuning with both flux and charge. The JPSQ is explicitly designed to realize a non-stoquastic, XX coupling in the absence of local qubit fields, thus overcoming an inherent limitation of all existing flux qubit based systems. This material is based upon work supported by the Defense Advanced Research Projects Agency and the Under Secretary of Defense for Research and Engineering under Air Force Contract No. FA8702-15-D-0001. Any opinions, findings, conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Under Secretary of Defense for Research and Engineering and Defense Advanced Research Projects Agency. |
Wednesday, March 8, 2023 8:48AM - 9:00AM |
M75.00003: Quantum stabilizers implemented with superconducting hardware Yebin Liu, Kenneth R Dodge, Bradley G Cole, Abigail Shearrow, Emma Brann, Matthew Snyder, Andrey Klots, Lev Ioffe, Robert McDermott, B.L.T. Plourde Quantum stabilizer operations play an important role in quantum error correction and are typically implemented in software-controlled entangling gates and measurements of groups of qubits. Alternatively, qubits can be designed so that the Hamiltonian includes terms that corresponds directly to stabilizers for protecting quantum information. In this talk, we demonstrate such a hardware implementation of stabilizers in a superconducting circuit based on concatenation of π-periodic Josephson elements. With local on-chip flux- and charge-biasing, we observe a flattening of the transition between the computational states with respect to flux that is exponential in the number of frustrated plaquette elements, in close agreement with our numerical modeling. |
Wednesday, March 8, 2023 9:00AM - 9:12AM |
M75.00004: Characterizing the Capacitance of Josephson Junctions for Topologically Protected Qubits Bradley G Cole, Yebin Liu, Kenneth R Dodge, Abigail Shearrow, Emma Brann, Matthew Snyder, Andrey Klots, Lev Ioffe, Robert McDermott, B.L.T. Plourde Recent measurements and modeling of quantum stabilizers implemented with superconducting hardware have shown that the concatenation of π-periodic Josephson elements can lead to protection against dephasing from flux noise that is exponential in the number of such elements. However, the Josephson junctions that are used in these elements require much higher Josephson and charging energies than traditional superconducting qubits. In this regime, the simultaneously large Josephson and charging energies result in a large junction plasma frequency, which can approach the superconducting gap, particularly for the Al electrodes that are commonly used in qubits. This results in an extra electronic capacitance contribution from quasiparticles on top of the conventional geometric capacitance. This excess capacitance causes a reduction in the junction charging energy below the level required for the π-periodic Josephson elements. We use measurements of the self-resonance steps on the IV curves of dc SQUIDs to characterize this electronic capacitance contribution as a function of critical current density and the superconducting gap. Junctions formed from electrodes with a larger superconducting gap should mitigate this effect for reaching the required regime for topological protection. |
Wednesday, March 8, 2023 9:12AM - 9:24AM |
M75.00005: Toward implementation of protected charge-parity qubits Abigail Shearrow, Emma Brann, Matthew Snyder, Kenneth R Dodge, Yebin Liu, Bradley G Cole, Andrey Klots, Lev B Ioffe, Britton L Plourde, Robert McDermott Topologically protected qubits are an area of growing interest and active research, with the potential for orders-of-magnitude improvements in coherence compared to conventional qubits. One such protected qubit is the charge-parity (C-parity) qubit, which consists of a pi-periodic Josephson element shunted by a large capacitance. Here, we implement imperfect pi-elements as "plaquettes" consisting of two arms in parallel, each arm incorporating a small-area Josephson junction in series with a large inductor. When the plaquette is biased at Φ0/2, the first harmonic of the Josephson energy is suppressed and the second harmonic, which is proportional to cos(2φ), remains. While individual plaquettes are not protected, protection scales exponentially with the number of plaquettes concatenated in series. In this talk we describe the design, fabrication, and characterization of a three-plaquette device. |
Wednesday, March 8, 2023 9:24AM - 9:36AM |
M75.00006: Measurement of the soft 0-pi qubit with small junction and inductive energies Junyoung An, Agustin Di Paolo, Ilan T Rosen, Roni Winik, Leon Ding, Max Hays, Alexander Melville, Bethany Huffman, David K Kim, Mollie E Schwartz, Terry P Orlando, Simon Gustavsson, Jeffrey A Grover, Kyle Serniak, William D Oliver Optimization of the soft 0-pi qubit requires a design space trade-off between noise protection and inductive leakage to neighboring states. In this talk, we present preliminary measurement results of a soft 0-pi qubit with small EJ and EL. While this parameter regime could be preferable in reducing leakage to neighboring states during gate operation, it could lead to smaller relaxation protection between the two logical states of the qubit. Additionally, we expect to achieve coherent qubit control using a Raman transition with an ancillary level located at relatively lower frequency. To measure the soft 0-pi qubit in this regime, we first employed an offset-charge calibration technique based on the variance of two quasiparticle parity states in the I-Q plane. Next, we show spectroscopy measurements together with a fit to a soft zero-pi qubit Hamiltonian. Finally, we explain the current challenges and the outlook to move beyond the limitations of the soft 0-pi qubit. |
Wednesday, March 8, 2023 9:36AM - 9:48AM |
M75.00007: Simple two qubit gates for the 0-π qubit Zhenxing Liu, Joshua L Combes The 0 − π qubit is an attractive candidate for a next generation superconducting qubit and has been experimentally realized in the “soft’’ 0 – π regime. We show how to connect the nodes of two 0− π circuits in order to achieve any desired coupling between any qubit degrees of freedom. This coupling allows us to construct two qubit gates. We will discuss the tradeoffs that arise between protection, circuit complexity, and gate times. |
Wednesday, March 8, 2023 9:48AM - 10:00AM |
M75.00008: A 0-pi qubit with in-situ tunable protection and control Farid Hassani Bijarbooneh The 0-pi qubit is one of the very few known superconducting circuit types that offers exponential protection from both phase and bit flip errors simultaneously. This feature comes at the cost of complex readout and control, which was shown experimentally in [1]. Here, we propose a way to break the circuit symmetry, the key reason for the protection, to momentarily restore the ability to control and manipulate the qubit without the use of ancillary levels. An asymmetry in capacitances and inductances in the 0-pi circuit are detrimental since they lead to coupling of the protected state to the thermally occupied parasitic mode of the circuit [2]. However, here we try to exploit a controlled asymmetry in Josephson energies and show that this can be used as a tunable coupler between the protected states. In the future, this should allow to perform gate operations by dynamically controlling the asymmetry instead of driving the protected transition with microwave pulses. Therefore, we believe that the proposed method can make the use of protected qubits more practical in experimental realizations of quantum computing. |
Wednesday, March 8, 2023 10:00AM - 10:12AM |
M75.00009: Designing improved zero-pi qubits using small-area capacitors Ilan Rosen, Junyoung An, Agustin Di Paolo, Leon Ding, Max Hays, Thomas M Hazard, Kate Azar, Alexander Melville, Bethany M Niedzielski, Katrina Silwa, Mollie E Schwartz, Jonilyn L Yoder, Jeffrey A Grover, Kyle Serniak, William D Oliver The “hard” zero-pi qubit regime—a zero-pi qubit exponentially immune to decoherence—is inaccessible due, in part, to the large capacitance to ground of extant devices. Replacing coplanar capacitors with parallel-plate capacitors, which have dramatically smaller footprints [1, 2], reduces the ground capacitance and extends the accessible regime of present “soft” zero-pi qubits. Here, we show that the newly-accessible parameter regime enables a device with increased immunity to decoherence. We discuss potential design flaws and parameter regimes that need be avoided. Lastly, we discuss new opportunities for qubit control and further device improvements. |
Wednesday, March 8, 2023 10:12AM - 10:24AM |
M75.00010: Overcoming barriers: Fast control of a qubit with variable protection Svend Krøjer, Anders Enevold Dahl, Kasper Sangild Christensen, Morten Kjaergaard, Karsten Flensberg Fast, high fidelity control of protected superconducting qubits is fundamentally challenging due to their inherent insensitivity. To achieve high coherence and fast control simultaneously, we propose to use qubits with a variable level of T1-protection. In this way, fast gates can be performed using traditional microwave pulse techniques in the unprotected regime while the qubits enjoy extended relaxation times when idling in the protected regime. To test the performance of such a scheme, we propose a simple T1-protected qubit design, the double-shunted flux qubit (DSFQ), a variation of the capacitively shunted flux qubit, where the level of protection is controlled through a single tunable junction. We show numerically that the overhead due to tuning in and out of protection is minimal and that both single- and two-qubit gates can be performed with high fidelity without occupying the low coherence, non-computational states. |
Wednesday, March 8, 2023 10:24AM - 10:36AM |
M75.00011: Controlling the protected soft zero-pi qubit Anjali Premkumar, András Gyenis, Pranav S Mundada, Sara F Sussman, Xanthe Croot, Jens Koch, Andrew A Houck The soft zero-pi circuit [1, 2, 3] has shown experimental evidence of protection against relaxation and dephasing, making it a promising candidate for high-fidelity quantum processing. Here, we show improved Ramsey dephasing times resulting from a larger ratio of the charging energies for the two participating modes, pushing the zero-pi further into its protected regime. We review possible gate schemes for the zero-pi, emphasizing the challenges of realizing two-tone Raman gates in protected superconducting qubits. |
Wednesday, March 8, 2023 10:36AM - 10:48AM |
M75.00012: Qubit readout with a non-linear cavity coupled to a transmon qubit via direct cross-Kerr coupling Kishor V Salunkhe, Madhavi Chand, Meghan P Patankar, Rajamani Vijayaraghavan The multimodal circuit nicknamed Quantromon has two orthogonal modes: a transmon qubit and a linear oscillator coupled to each other via direct cross-Kerr coupling. An integrated qubit-cavity system is realized using these modes with the linear oscillator playing the role of the readout cavity. We previously demonstrated a high measurement fidelity of 97.63% without using the Josephson parametric amplifier due to the possibility of using higher photon numbers in the Quantromon. In this work, we replace the linear oscillator mode with a non-linear Josephson junction-based oscillator. This enables the possibility of accessing the parametric amplification and bifurcation regime of the non-linear oscillator for integrated amplification in the measurement cavity. Previous experiments have explored integrated amplification using a non-linear readout cavity e.g. the quantronium qubit in the charging regime [1] and a transmon qubit coupled transversely to a non-linear oscillator [2]. More recently, a transmon qubit readout using in-situ bifurcation of a nonlinear dissipative polariton has been demonstrated [3]. We will discuss the different operating regimes of our device and present experimental data demonstrating qubit measurement. We will also compare our technique and results with the others mentioned above and discuss key similarities and differences. |
Wednesday, March 8, 2023 10:48AM - 11:00AM |
M75.00013: Purcell protection and crosstalk reduction using multimode superconducting circuits Frederik Pfeiffer, Christian Schweizer, Gerhard Huber, Leon Koch, Niklas Bruckmoser, Stefan Filipp Superconducting qubits are promising candidates for quantum computation due to their long coherence times and high-fidelity control. However, coupling to readout circuits and neighboring qubits can limit qubit performance through Purcell decay and crosstalk. To protect the qubit from these effects, we propose a multimode superconducting circuit composed of three superconducting islands coupled to a central island via Josephson junctions. When the capacitance to the center island is small, the circuit accommodates two modes in the 1-10 GHz frequency range with a large cross-Kerr interaction: one mode decouples from other circuit elements and is used as a protected logical mode; the other mode is used to mediate couplings to the readout resonator and other qubits. Replacing one of the junctions with a SQUID makes the mediating mode flux tunable. By simultaneously driving the tunable modes of adjacent multimode circuits, we introduce conditional phases on the logical modes, resulting in a CPHASE gate. Numerical simulations of coherent dynamics suggest gate fidelities of 99.9 % for a gate time of 100 ns, up to single qubit rotations. |
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