We analyze a single-shot readout for superconducting qubits via the controlled catch, dispersion, and release of a microwave field. A tunable coupler is used to decouple the microwave resonator from the transmission line during the dispersive qubit-resonator interaction, thus circumventing damping from the Purcell effect. We show that if the qubit frequency tuning is sufficiently adiabatic, a fast high-fidelity qubit readout is possible even in the strongly nonlinear dispersive regime. Interestingly, the Jaynes-Cummings nonlinearity leads to the quadrature squeezing of the resonator field below the standard quantum limit, resulting in a significant decrease of the measurement error.PACS numbers: 03.67. Lx, 03.65.Yz, 42.50.Pq, 85.25.Cp A fast high-fidelity qubit readout plays an important role in quantum information processing. For superconducting qubits various nonlinear processes have been used to realize a singleshot readout [1][2][3][4][5][6]. The linear dispersive readout in the circuit quantum electrodynamics (cQED) setup [7,8] became sufficiently sensitive for the single-shot qubit measurement only recently [9,10], with development of near-quantum-limited superconducting parametric amplifiers [9][10][11]. In particular, readout fidelity of 94% for flux qubits [9] and 97% for transmon qubits [10] has been realized (see also [12]). With increasing coherence time of superconducting qubits into 10-100 µs range [13,14], fast high-fidelity readout becomes practically important, for example, for reaching the threshold of quantum error correction codes [15], for which the desired readout time is less than 100 ns, with fidelity above 99%.A significant source of error in the currently available cQED readout schemes is the Purcell effect [16] -the cavityinduced relaxation of the qubit due to the always-on coupling between the resonator and the outgoing transmission line. The Purcell effect can be reduced by increasing the qubit-resonator detuning; however, this reduces the dispersive interaction and increases measurement time. Several proposals to overcome the Purcell effect have been put forward, including the use of the Purcell filter [17] and the use of a Purcell-protected qubit [18]. Here we propose and analyze a cQED scheme which avoids the Purcell effect altogether by decoupling the resonator from the transmission line during the dispersive qubitresonator interaction.Similar to the standard cQED measurement [7][8][9][10], in our method (Fig. 1) the qubit state affects the dispersive shift of the resonator frequency, that in turn changes the phase of the microwave field in the resonator, which is then measured via homodyne detection. However, instead of measuring continuously, we perform a sequence of three operations: "catch", "disperse", and "release" of the microwave field. During the first two stages a tunable coupler decouples the outgoing transmission line from the resonator (we assume using the coupler recently realized in [19]; see also [20]). This automatically eliminates the problems associated with...
Using circuit QED, we consider the measurement of a superconducting transmon qubit via a coupled microwave resonator. For ideally dispersive coupling, ringing up the resonator produces coherent states with frequencies matched to transmon energy states. Realistic coupling is not ideally dispersive, however, so transmon-resonator energy levels hybridize into joint eigenstate ladders of the Jaynes-Cummings type. Previous work has shown that ringing up the resonator approximately respects this ladder structure to produce a coherent state in the eigenbasis (a dressed coherent state). We numerically investigate the validity of this coherent state approximation to find two primary deviations. First, resonator ring-up leaks small stray populations into eigenstate ladders corresponding to different transmon states. Second, within an eigenstate ladder the transmon nonlinearity shears the coherent state as it evolves. We then show that the next natural approximation for this sheared state in the eigenbasis is a dressed squeezed state, and derive simple evolution equations for such states using a hybrid phase-Fock-space description.
We analyze the transfer of a quantum state between two resonators connected by a superconducting transmission line. Nearly perfect state-transfer efficiency can be achieved by using adjustable couplers and destructive interference to cancel the back-reflection into the transmission line at the receiving coupler. We show that the transfer protocol is robust to parameter variations affecting the transmission amplitudes of the couplers. We also show that the effects of Gaussian filtering, pulse-shape noise, and multiple reflections on the transfer efficiency are insignificant. However, the transfer protocol is very sensitive to frequency mismatch between the two resonators. Moreover, the tunable coupler we considered produces time-varying frequency detuning caused by the changing coupling. This detuning requires an active frequency compensation with an accuracy better than 90% to yield the transfer efficiency above 99%.Comment: 25 pages, 17 figures; published versio
We analyze a single-shot readout for superconducting qubits via the controlled catch, dispersion, and release of a microwave field. A tunable coupler is used to decouple the microwave resonator from the transmission line during the dispersive qubit-resonator interaction, thus circumventing damping from the Purcell effect. We show that if the qubit frequency tuning is sufficiently adiabatic, a fast high-fidelity qubit readout is possible even in the strongly nonlinear dispersive regime. Interestingly, the Jaynes-Cummings nonlinearity leads to the quadrature squeezing of the resonator field below the standard quantum limit, resulting in a significant decrease of the measurement error.
No abstract
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2025 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.