Initial experimental results on a superconducting-qubit reset based on photon-assisted quasiparticle tunneling

Abstract

We present here our recent results on qubit reset scheme based on a quantum-circuit refrigerator (QCR). In particular, we use the photon-assisted quasiparticle tunneling through a superconductor–insulator–normal-metal–insulator–superconductor junction to controllably decrease the energy relaxation time of the qubit during the QCR operation. In our experiment, we use a transmon qubit with dispersive readout. The QCR is capacitively coupled to the qubit through its normal-metal island. We employ rapid, square-shaped QCR control voltage pulses with durations in the range of 2–350 ns and a variety of amplitudes to optimize the reset time and fidelity. Consequently, we reach a qubit ground-state probability of roughly 97% with 80-ns pulses starting from the first excited state. The qubit state probability is extracted from averaged readout signal, where the calibration is based on Rabi oscillations, thus not distinguishing the residual thermal population of the qubit.

Optimized emulation of quantum magnetometry via superconducting qubits

“…Since the goal of this work is to estimate the best sensitivity that can be obtained using state-of-the-art devices, we consider a fast reset approximately equal to 100 ns [42], a fast H gate approximately equal to 50 ns, and a fast measurement approximately equal to 250 ns [43]. Thus, a distinct majority of the total time of the magnetometry will be contributed by the total interaction time t sum .…”

“…The total magnetometry time t sum consists of an interaction time and a qubit manipulation time t p , including reset, gates, and readout duration. Reset takes approximately 100 ns [42], gates take approximately 50 ns, and readout takes approximately 250 ns [43], resulting in a total manipulation time of t p ∼ 500 ns. We divide all k max × n rep measurements in chunks of size n rep and, starting from t 0 , we assign a single measurement with the shortest t k to an available qubit.…”

Exceptional-point-assisted entanglement, squeezing, and reset in a chain of three superconducting resonators

“…In circuit quantum electrodynamics (cQED), for example, efforts have been made to integrate devices with in-situ-tunable dissipation to prepare specific quantum states [5][6][7][8][9][10][11][12], produce fast reset [13][14][15][16][17][18][19][20][21][22][23][24], and to exploit the potential benefits of open-system degeneracies, referred to as exceptional points (EPs) [17,21,[25][26][27][28][29]. In contrast to Hermitian degeneracies, EPs induce the coalescence of eigenvalues and eigenvectors of the dynamical matrix governing the open-system evolution leading to critical dynamics manifested by polynomial solutions in time [30,31].…”

Many-excitation removal of a transmon qubit using a single-junction quantum-circuit refrigerator and a two-tone microwave drive

“…Proper control of the bias voltage through this junction results in the incoherent removal or injection of photons into its surroundings, effectively rendering the QCR a controllable environment for its coupled circuitry. Previous experimental studies with the QCR have already shown a speedup of dissipation up to almost four orders of magnitude at the nanosecond scale 15,20 , yielding promising insights into its potential for reset applications. Therefore, integrating the QCR into the hardware of superconducting-based quantum computers may enable its practical utilization in active reset protocols, as we demonstrate in this work.…”

“…To evade the initialization errors arising from unwanted excitation to higher eigenstates and the feedback imposed by measurement-based protocols, parameter tunability plays an important role in reset strategies 5 . Recent reset schemes for superconducting circuits employ this tunability through different ways, such as frequency modulation 6,7 , all-microwave control [8][9][10] , and engineered environments [11][12][13][14][15] .…”