I am going to post here all newly submitted articles on the arXiv related to superconducting circuits. If your article has been accidentally forgotten, feel free to contact me
15
Feb
2023
Shortcuts to adiabaticity in superconducting circuits for fast multi-partite state generation
Shortcuts to adiabaticity provides a flexible method to accelerate and improve a quantum control task beyond adiabatic criteria. Here we propose the reverse-engineering approach to
design the longitudinal coupling between a set of qubits coupled to several field modes, for achieving a fast generation of multi-partite quantum gates in photonic or qubit-based architecture. We show that the enhancing generation time is at the nanosecond scale that does not scale with the number of system components. In addition, our protocol does not suffer noticeable detrimental effects due to the dissipative dynamics. Finally, the possible implementation is discussed with the state-of-the-art circuit quantum electrodynamics architecture.
Microwave amplification via interfering multi-photon processes in a half-waveguide quantum electrodynamics system
We investigate the amplification of a microwave probe signal by a superconducting artificial atom, a transmon, strongly coupled to the end of a one-dimensional semi-infinite transmission
line. The end of the transmission line acts as a mirror for microwave fields. Due to the weak anharmonicity of the artificial atom, a strong pump field creates multi-photon excitations among the dressed states. Transitions between these dressed states, Rabi sidebands, give rise to either amplification or attenuation of the weak probe. We obtain a maximum amplitude amplification of about 18 %, higher than in any previous experiment with a single artificial atom, due to constructive interference between Rabi sidebands. We also characterize the noise properties of the system by measuring the spectrum of spontaneous emission.
14
Feb
2023
Autonomous error correction of a single logical qubit using two transmons
Large-scale quantum computers will inevitably need quantum error correction to protect information against decoherence. Traditional error correction typically requires many qubits,
along with high-efficiency error syndrome measurement and real-time feedback. Autonomous quantum error correction (AQEC) instead uses steady-state bath engineering to perform the correction in a hardware-efficient manner. We realize an AQEC scheme, implemented with only two transmon qubits in a 2D scalable architecture, that actively corrects single-photon loss and passively suppresses low-frequency dephasing using six microwave drives. Compared to uncorrected encoding, factors of 2.0, 5.1, and 1.4 improvements are experimentally witnessed for the logical zero, one, and superposition states. Our results show the potential of implementing hardware-efficient AQEC to enhance the reliability of a transmon-based quantum information processor.
All-microwave manipulation of superconducting qubits with a fixed-frequency transmon coupler
All-microwave control of fixed-frequency superconducting quantum computing circuits is advantageous for minimizing the noise channels and wiring costs. Here we introduce a swap interaction
between two data transmons assisted by the third-order nonlinearity of a coupler transmon under a microwave drive. We model the interaction analytically and numerically and use it to implement an all-microwave controlled-Z gate. The gate based on the coupler-assisted swap transition maintains high drive efficiency and small residual interaction over a wide range of detuning between the data transmons.
13
Feb
2023
Two-level approximation of transmons in quantum quench experiments
Quantum quench is a typical protocol in the study of nonequilibrium dynamics of quantum many-body systems. Recently a number of experiments with superconducting transmon qubits are
reported, in which the celebrated spin and hard-core Bose-Hubbard models with two energy levels on individual sites are used. The transmons have nonequidistant energy levels, among which the two lowest levels form the computational subspace. In this work, we numerically simulate realistic experiments of quantum quench dynamics and discuss the applicability of the two-level approximation for the multilevel transmons. We calculate the fidelity decay (i.e., the time-dependent overlap of evolving wave functions) due to the state leakage to transmon high energy levels for two kinds of quantum quench experiments with time reversal and time evolution in one direction, respectively. We present the results of the fidelity decay for different system Hamiltonians with various initial state, qubit coupling strength, and external driving. The extent to which the spin and hard-core Bose-Hubbard models can be applied under various circumstances is discussed and compared with experimental observations. Our work provides a precise way to assess the two-level approximation of transmons in quantum quench experiments and shows that good approximation is reachable using the present-day superconducting circuit architecture.
A superconducting quantum memory with tens of milliseconds coherence time
Storing quantum information for an extended period of time is essential for running quantum algorithms with low errors. Currently, superconducting quantum memories have coherence times
of a few milliseconds, and surpassing this performance has remained an outstanding challenge. In this work, we report a qubit encoded in a novel superconducting cavity with a coherence time of 34 ms, an improvement of over an order of magnitude compared to previous demonstrations. We use this long-lived quantum memory to store a Schrödinger cat state with a record size of 1024 photons, indicating the cavity’s potential for bosonic quantum error correction.
09
Feb
2023
Demonstration of deterministic SWAP gate between superconducting and frequency-encoded microwave-photon qubits
The number of superconducting qubits contained in a single quantum processor is increasing steadily. However, to realize a truly useful quantum computer, it is inevitable to increase
the number of qubits much further by distributing quantum information among distant processors using flying qubits. Here, we demonstrate a key element towards this goal, namely, a SWAP gate between the superconducting-atom and microwave-photon qubits. The working principle of this gate is the single-photon Raman interaction, which results from strong interference in one-dimensional optical systems and enables a high gate fidelity insensitively to the pulse shape of the photon qubit, by simply bouncing the photon qubit at a cavity attached to the atom qubit. We confirm the bidirectional quantum state transfer between the atom and photon qubits. The averaged fidelity of the photon-to-atom (atom-to-photon) state transfer reaches 0.829 (0.801), limited mainly by the energy relaxation time of the atom qubit. The present atom-photon gate, equipped with an in situ tunability of the gate type, would enable various applications in distributed quantum computation using superconducting qubits and microwave photons.
Characterising Polariton States in Non-Dispersive Regime of Circuit Quantum Electrodynamics
A superconducting qubit coupled to a read-out resonator is currently the building block of multiple quantum computing as well as quantum optics experiments. A typical qubit-resonator
system is coupled in the dispersive regime, where the detuning between qubit and resonator is much greater than the coupling between them. In this work, we fabricated and measured a superconducting transmon-resonator system in the non-dispersive regime. The dressed states formed by the mixing of the bare qubit and resonator states can be further mixed by applying a drive on the qubit, leading to the formation of polariton states. We report experimental studies of transitions between polariton states at varying driving powers and frequencies and show how the non-dispersive coupling of the higher levels of the qubit-resonator system modifies the polariton eigenstates and the corresponding transition frequencies. We also report close agreement with numerical results obtained from a driven Jaynes-Cummings Model beyond the dispersive regime.
08
Feb
2023
Simulation of Kitaev model using one-dimensional chain of superconducting qubits and environmental effect on topological states
Kitaev fermionic chain is one of the important physical models for studying topological physics and quantum computing. We here propose an approach to simulate the one-dimensional Kitaev
model by a chain of superconducting qubit circuits. Furthermore, we study the environmental effect on topological quantum states of the Kitaev model. Besides the independent environment surrounding each qubit, we also consider the common environment shared by two nearest neighboring qubits. Such common environment can result in an effective non-Hermitian dissipative coupling between two qubits. Through theoretical analysis and numerical calculations, we show that the common environment can significantly change properties of topological states in contrast to the independent environment. In addition, we also find that dissipative couplings at the edges of the chain can be used to more easily tune the topological properties of the system than those at other positions. Our study may open a new way to explore topological quantum phase transition and various environmental effects on topological physics using superconducting qubit circuits.
Gatemon qubit based on a thin InAs-Al hybrid nanowire
We study a gate-tunable superconducting qubit (gatemon) based on a thin InAs-Al hybrid nanowire. Using a gate voltage to control its Josephson energy, the gatemon can reach the strong
coupling regime to a microwave cavity. In the dispersive regime, we extract the energy relaxation time T1∼0.56 μs and the dephasing time T∗2∼0.38 μs. Since thin InAs-Al nanowires can have fewer or single sub-band occupation and recent transport experiment shows the existence of nearly quantized zero-bias conductance peaks, our result holds relevancy for detecting Majorana zero modes in thin InAs-Al nanowires using circuit quantum electrodynamics.