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 Y73: Superconducting Qubits: Novel Qubit and Gate Concepts |
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Sponsoring Units: DQI Chair: Patrick Winkel, Yale University Room: Room 405 |
Friday, March 10, 2023 8:00AM - 8:12AM |
Y73.00001: Two superconducting artificial atoms ultrastrongly coupled to a single mode resonator Akiyoshi Tomonaga, Hiroto Mukai, Jaw-Shen Tsai We report a experimental result of two artificial atoms (superconducting flux qubits) coupling via a single mode superconducting LC resonator. In the system, each artificial atom couple to resonator as strong as g (coupling frequency) ~ 0.5w (resonator frequency). In the experiment, we biased atom 1 and 2 to be near to the optimal point. Thus, we can make situation that the resonator energy = the energy of atom 1 + the energy of atom 2. In the spectrum of a ultrastrongly coupled system, we can see many energy transition signals in S21 measurement. To fit the spectrum, information of the frequency in each branch is required. Thereby, to obtain peak points we used image processing by Python [1]. Our circuit model described spectrum well. In this level of coupling strength, we can see the anti-splitting between a one photon state and a two artificial atoms excited state. In other words, a single photon in resonator can simultaneously excite two coupled atoms [2]. |
Friday, March 10, 2023 8:12AM - 8:24AM |
Y73.00002: Emulating 2 qubits with a 4-level superconducting transmon Shuxiang Cao, Mustafa S Bakr, Giulio Campanaro, Simone D Fasciati, James F Wills, Boris Shteynas, Vivek Chidambaram, Peter J Leek Near-term quantum algorithms for quantum chemistry require the quantum device to provide a sufficiently large Hilbert space to encode the chemistry target. Traditionally such a large Hilbert space is achieved with many two-level systems. Utilizing additional levels of the quantum system would be beneficial in reducing hardware complexity. Here we present a variational quantum eigensolver using four levels of a superconducting transmon device. We use this 4-level system to emulate a two-qubit system and demonstrate solving hydrogen molecule eigenstates. |
Friday, March 10, 2023 8:24AM - 8:36AM |
Y73.00003: Designing and driving superconducting qutrit processors Rayleigh Parker, Zihao Wang, Machiel Blok Computations with quantum three-level systems (qutrits) offer potential advantages over those with qubits, and they are available on current superconducting quantum processors with very little additional overhead. Despite recent progress in improving superconducting qutrit processors, research into optimizing qutrit gate fidelities and coherence times still lags behind similar research for two-level systems. In this talk, we discuss ongoing efforts to understand and mitigate coherent and incoherent errors specific to quantum information processing with transmon qutrits. First, we present an experimental investigation into scaling of higher-level coherence times with circuit parameters such as EJ/EC and surface participation ratios. Second, we apply analytical perturbative methods to address coherent errors arising from simultaneous driving of two transition frequencies. By studying and mitigating errors specific to qutrit processors, this research aims to realize high-fidelity qutrit control. |
Friday, March 10, 2023 8:36AM - 8:48AM |
Y73.00004: High-Fidelity Qutrit Entanglement in Superconducting Circuits Noah Goss, Long B Nguyen, Ravi K Naik, Alexis Morvan, Brian Marinelli, Brad Mitchell, John Mark Kreikebaum, Larry Chen, Christian Jünger, David I Santiago, Irfan Siddiqi The workhorse qubit of modern superconducting systems – the transmon – has readily addressable higher states making it also a natural platform for qutrit operation. Provided high-fidelity multi-qutrit control, the larger, more connected computational space leveraged in a ternary approach to quantum computation can enable improvements to quantum simulation and error correction. Nonetheless, a significant impediment to realizing effective qutrit processing in a superconducting platform has been the ability to generate high-fidelity qutrit entangling gates. Recently, utilizing the Differential AC-Stark effect, we have demonstrated a dynamic cross-Kerr interaction between two fixed-frequency transmon qutrits and leveraged it to generate high-fidelity, maximally-entangling qutrit controlled-phase gates. Additionally, enabling coherent control over the full multi-qutrit Hilbert space allows one to compactly generate multi-controlled qubit entangling gates and achieve greater flexibility in generating two-qubit gates. In this talk, we present advanced control and characterization techniques in transmon qutrits that we leverage for high-fidelity qutrit entangling operations to improve both binary and ternary approaches to quantum computation. |
Friday, March 10, 2023 8:48AM - 9:00AM |
Y73.00005: Novel superconducting qubit concepts for higher temperature quantum information processing John H Miller, Martha Y Villagran, Johnathan O Sanderson, Jarek Wosik The ability to operate quantum computers at higher temperatures vs. today’s transmon-based systems would greatly expand their range of applications. This could be achieved by increasing resonance frequencies and/or utilizing collective modes more robust against decoherence. We discuss several nonlinear resonator concepts in which the roles of linear and nonlinear elements are reversed vs. the transmon. The simplest version is a nonlinear LC resonator in which the superconducting inductor is linear, while a nonlinear capacitor is enabled by a nonlinear dielectric. Due to progress in 5/6G, some ferroelectric materials may enable operation of a nonlinear dielectric – superconductor qubit at hundreds of GHz. Other nonlinear dielectrics include quantum paraelectrics, such as SrTiO3 and KTaO3, and charge density wave materials. These are intriguing due to collective modes resulting from macroscopically occupied states. Additional concepts include half- or quarter-wavelength resonators employing nonlinear dielectrics. Possible signatures of collective behavior include coherent many-body Rabi oscillations or super-Rabi oscillations. |
Friday, March 10, 2023 9:00AM - 9:12AM |
Y73.00006: Resonator-free readout of a unimon Vasilii Vadimov, Eric Hyyppä, Suman Kundu, Mikko Möttönen, Olavi Kiuru, Akseli Mäkinen, Alessandro Landra, Caspar Ockeloen-Korppi, Wei Liu, Tianyi Li, Jian Ma, Johannes Heinsoo, Juha Hassel, Kuan Y Tan Unimon [1] is a recently invented high-anharmonicity superconducting qubit, which is immune to low-frequency charge noise owing to its island-free design. It presents a grounded λ/2 coplanar waveguide resonator with a Josephson junction in the middle of the central conductor. Anharmonicity of this qubit is enhanced by a partial cancellation of the inductive energy of the central conductor by the Josephson energy of the flux-biased junction. Due to the distributed nature of the unimon, it is essentially multi-mode. For a symmetric unimon with the junction exactly in the middle of the central conductor only half of these modes are non-linear and can be used for the quantum computation while the rest are linear. However, these intrinsic linear modes can be used for dispersive readout of the unimon without introducing an additional resonator. The required coupling between the linear and nonlinear modes can be achieved by making the unimon slightly asymmetric. Coupling of the readout mode to the external transmission line can be implemented via two-point coupler which protects the qubit state from dissipation. This work presents an important step for development of quantum logic for novel superconducting qubits. |
Friday, March 10, 2023 9:12AM - 9:24AM |
Y73.00007: Qubit Demonstrations at Frequencies Above Ten Gigahertz Adam J Sirois, Manuel A Castellanos-Beltran, Peter Hopkins, David Olaya, John P Biesecker, Samuel P Benz Typical superconducting quantum information technologies are designed to operate in the 4 GHz to 8 GHz frequency range. Yet, there are advantages to operating at higher frequencies. Namely, there are less stringent constraints on cryogenic operating temperature as well as area scaling advantages. We present our designs and measurement results on higher frequency qubits and associated electronics, including a systematic study of materials losses, qubit designs, and measurement challenges. We focus on frequencies from 10 GHz to 30 GHz, and present a roadmap to achieving higher frequency qubits operating at temperatures approaching 1 K . Additionally, we report on schemes to up-convert control signals from lower frequencies using kinetic inductance structures. |
Friday, March 10, 2023 9:24AM - 9:36AM |
Y73.00008: Spectral kissing and its dynamical consequences in the squeezed Kerr-nonlinear oscillator Jorge Chavez, Talía Lezama Mergold Love, Rodrigo G Cortinas, Jayameenakshi Venkatraman, Michel H Devoret, Victor S Batista, Francisco Pérez-Bernal, Lea F Santos Transmon qubits are the predominant element in circuit-based quantum information processing due to their controllability and ease of engineering implementation. But more than qubits, transmons are multilevel nonlinear oscillators that can be employed in the discovery of new fundamental physics. In this talk, we show that they can be used as simulators of excited state quantum phase transitions (ESQPTs), which are generalizations of quantum phase transitions to excited states. The coalescence of pairs of adjacent energy levels (spectral kissing) recently observed with a squeezed Kerr oscillator is an ESQPT precursor. The classical limit of this system explains the origin of the quantum critical point and its consequences for the quantum dynamics, which includes both the fast scrambling of quantum information, characterized by the exponential growth of out-of- time-ordered correlators, and the slow evolution of the survival probability at initial times, caused by the localization of the energy eigenstates at the vicinity of the ESQPT. These signatures of ESQPT in the spectrum and in the quantum dynamics are simultaneously within reach for current superconducting circuits experiments. |
Friday, March 10, 2023 9:36AM - 9:48AM |
Y73.00009: Finite bandwidth gyrator on GKP-encoding circuit Stefanus E Tanuarta, Andrew C Doherty Rymarz et al. proposed a construction of a superconducting circuit whose ground states are the codewords of the GKP code. This was done by utilizing a non-reciprocal circuit element known as the gyrator. In this work, we will build on this work by implementing a finite bandwidth gyrator based on an impedance model built from temporal coupled-mode theory. We then study its effects on the ground states of the circuit Hamiltonian. |
Friday, March 10, 2023 9:48AM - 10:00AM |
Y73.00010: Suppressing 1/f Magnetic Flux Noise in Superconducting Qubits with Weak Magnetic Fields (Part 1) David A Rower, Lamia Ateshian, Max Hays, Kyle Serniak, Lauren H Li, Bharath Kannan, Leon Ding, Dolev Bluvstein, Aziza Almanakly, Jochen Braumueller, David K Kim, Alexander Melville, Bethany M Niedzielski, Jonilyn L Yoder, Mollie E Schwartz, Terry P Orlando, Joel I Wang, Simon Gustavsson, Jeffrey A Grover, Riccardo Comin, William D Oliver The microscopic origin of 1/f magnetic flux noise in superconducting circuits has remained an open question for several decades, despite extensive experimental and theoretical investigation. One crucial missing piece to develop a microscopic theory of the noise mechanism is the response to external magnetic fields. We apply in-plane magnetic fields to flux qubits, and study flux-noise-limited dephasing. We observe an enhancement of spin-echo T2 in fields up to B = 100 G. We measure the flux noise spectrum directly over several decades, and observe the suppression of flux noise in the MHz range accompanied by an enhancement of flux noise below 1 Hz. These results constitute the first characterization of flux noise limited dephasing in applied magnetic fields, which we hope will help to inform a complete microscopic theory of 1/f flux noise in superconducting circuits. |
Friday, March 10, 2023 10:00AM - 10:12AM |
Y73.00011: Suppressing 1/f Magnetic Flux Noise in Superconducting Qubits with Weak Magnetic Fields (Part 2) Lamia Ateshian, David A Rower, Max Hays, Kyle Serniak, Lauren H Li, Bharath Kannan, Leon Ding, Dolev Bluvstein, Aziza Almanakly, Jochen Braumueller, David K Kim, Alexander Melville, Bethany M Niedzielski, Jonilyn L Yoder, Mollie E Schwartz, Terry P Orlando, Joel I Wang, Simon Gustavsson, Jeffrey A Grover, Riccardo Comin, William D Oliver 1/f magnetic flux noise is known to limit the coherence of superconducting qubits, yet its microscopic origin has remained an open question for decades. While many experimental and theoretical studies have sought to elucidate the physical mechanism, one missing but critical characterization is the noise response to magnetic fields. Here we present the first study of flux-noise-limited dephasing and 1/f noise spectroscopy in superconducting flux qubits subjected to in-plane magnetic fields up to B = 100 G. Notably, in addition to an increase in noise below 1 Hz, we observe a suppression of flux noise in the MHz range accompanied by an enhancement of echo T2 up to 100 G. We also report initial observations of interesting features including magnetic-field-specific avoided crossings in the qubit spectrum and a tri-fold splitting of the qubit frequency at certain magnetic fields. This study presents a new experimental angle into the exploration of surface magnetic defects, and ultimately should help inform a complete microscopic theory of 1/f flux noise in superconducting circuits. |
Friday, March 10, 2023 10:12AM - 10:24AM |
Y73.00012: Theory of flux noise in the presence of an external magnetic field. Jose A Nava Aquino, Rogério de Sousa Impurity spins randomly distributed at the surfaces and interfaces of superconducting wires are known to cause flux noise in Superconducting Quantum Interference Devices (SQUIDs), providing a dominant mechanism for decoherence in flux-tunable superconducting qubits. Recently, we developed a second principles method that is able to compute flux noise from the microscopic Hamiltonian of interacting spins [1]. The method provides explicit numerical predictions for the flux noise power law observed in experiments, including its temperature dependence. |
Friday, March 10, 2023 10:24AM - 10:36AM |
Y73.00013: Fabrication of thin diamond membranes by Ne implantation Luca Basso, Pauli Kehayias, Jacob D Henshaw, Rong Cong, Michael Titze, Edward S Bielejec, Tzu-Ming Lu, Michael P Lilly, Andrew M Mounce Despite color centers in diamond represent a leading tool for quantum information science, an efficient and consistent integration of these diamond-based platform with other devices remains a challenge. Single-crystal, color-centers-enriched, nanoscale-thick diamond membranes could play an important role as layers in heterostructures devices, with applications ranging from nanophotonics to quantum sensing. A common top-down approach for membranes production is known as “smart-cut”: a diamond is implanted with He ions that form a graphitized layer below diamond surface, layer that is then etched to lift-off the resulting thin membrane from the diamond substrate. Due to the high ions flux fluence required, this process is extremely time-consuming. In this work, diamond membranes are produced by Ne implantation of a diamond substrate resulting in ~300 nm thick membranes formation. To find the graphitization threshold, different Ne flux fluences are tested. The implanted diamonds are characterized with SEM and TEM, while the quality of the resulting membrane is assessed by Raman and photoluminescence spectroscopy. Compared to He smart-cut, we showed that the use of a heavier ion like Ne results in a ten-fold decrease in fabrication time without affecting the membrane quality. |
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