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Physical Review A

Generation of cat states by a weak parametric drive and a transitionless tracking algorithm

Shuai Liu, Ye‐Hong Chen, Yu Wang, Yi‐Hao Kang, Zhi‐Cheng Shi, Jie Song, Yan Xia

Published Oct 20, 2022• 20 citations
Publisher

Abstract

In this paper, we present an experimentally feasible protocol to generate the cat states in the microwave resonator coupled to a superconducting qubit. The setup employs a detuned, time-dependent parametric drive to squeeze the resonator mode so that an adjustable qubit-resonator coupling strength can be obtained. Therefore, based on the transitionless tracking algorithm, we can design control pulses to generate the qubit-resonator entangled states with high fidelity in the laboratory frame. Then, the even and odd cat states can be further obtained by performing measurement on the superconducting qubit. Compared to the scheme [Chen et al., Phys. Rev. Lett. 126, 023602 (2021)], the present protocol is realized in the regime of weak parametric drive. In the case, squeezing-induced noise can be reduced so that the fidelity of the generated state can be improved. Numerical simulations indicate that the present protocol is well executed under experimentally available parameters. Thus, the protocol is feasible with the present state of the art in microwave superconducting circuits.

DOI
10.1103/physreva.106.042430

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In this paper, we present an experimentally feasible protocol to generate the cat states in the microwave resonator coupled to a superconducting qubit. The setup employs a detuned, time-dependent parametric drive to squeeze the resonator mode so that an adjustable qubit-resonator coupling strength can be obtained. Therefore, based on the transitionless tracking algorithm, we can design control pulses to generate the qubit-resonator entangled states with high fidelity in the laboratory frame. Then, the even and odd cat states can be further obtained by performing measurement on the superconducting qubit. Compared to the scheme [Chen et al., Phys. Rev. Lett. 126, 023602 (2021)], the present protocol is realized in the regime of weak parametric drive. In the case, squeezing-induced noise can be reduced so that the fidelity of the generated state can be improved. Numerical simulations indicate that the present protocol is well executed under experimentally available parameters. Thus, the protocol is feasible with the present state of the art in microwave superconducting circuits.
A dissipative method is proposed for generating the squeezed state of a microwave field in a superconducting transmission line resonator, which is coupled to a superconducting qubit. When the resonator is subject to the parametric driving, the qubit-resonator coupling can be exponentially enhanced. We show that the dissipation of the qubit as a resource can be used to produce and stabilize the single-mode squeezed state of the superconducting resonator at steady state. Compared with previous works, our scheme has the advantage that only a single drive is used for the quantum state preparation, which can simplify the experimental operations. Combined with the quantum interference effect, we also generalize our idea to the dissipative preparation of a two-mode squeezed state in two directly coupled superconducting resonators. The present work may have many potential applications in the field of quantum information processing with superconducting circuits.
We study controllable generation of two-mode-entangled states in a circuit QED setup, which consists of two spatially separated superconducting transmission line resonators and a single gap-tunable superconducting qubit. Two sharp coupling sidebands are induced when the artificial atom is suitably driven by a bichromatic microwave field. The two resonators can have squeezing-type interactions with the qubit via the coupling sidebands. If the two resonators are not degenerate, we show that the two resonators can be cooled down into the two-mode squeezed vacuum via dissipation of the qubit. The generation of the two-mode squeezed state is based on a dissipative state-engineering process, which explores the energy relaxation of the qubit as a resource. Moreover, the scheme does not need both the specific preparation of the initial state and the designed special dynamical process of the system. If the resonators are degenerate, we show that entangled coherent states of the resonators can be generated by use of the unitary dynamical evolution process of the system and the state-projection measurement. Moreover, macro entangled coherent states of the resonators with huge photons can in principle be created if the resonators and the qubit have sufficiently long lifetimes. The present scheme has two remarkable features: (1) only a single qubit is used in the generation of the two-mode squeezed state; and (2) the ultrastrong coupling condition and initializing the resonators in coherent states are not required. These make the present scheme more simple and feasible in experimental implementation.
In the circuit quantum electrodynamics architecture, both the resonance frequency and the coupling of superconducting qubits to microwave field modes can be controlled via external electric and magnetic fields to explore qubit-photon dynamics in a wide parameter range. Here, we experimentally demonstrate and analyze a scheme for tuning the coupling between a transmon qubit and a microwave resonator using a single coherent drive tone. We treat the transmon as a three-level system, with the qubit subspace defined by the ground and the second excited states. If the drive frequency matches the difference between the resonator and the qubit frequencies, a Jaynes-Cummings-type interaction is induced, which is tunable in both amplitude and phase. We show that coupling strengths of about 10 MHz can be achieved in our setup, limited only by the anharmonicity of the transmon qubit. This scheme has been successfully used to generate microwave photons with a controlled temporal shape [M. Pechal et al., Phys. Rev. X 4, 041010 (2014)] and can be directly implemented with superconducting quantum devices featuring larger anharmonicity for higher coupling strengths.
We propose a scheme to dissipatively stabilize superpositions of squeezed coherent states for single- and two-resonator modes in superconducting circuits, where a superconducting qubit is coupled to a single or two parametrically driven transmission-line resonators with different circuit designs. A modulated magnetic flux applied to the qubit can periodically break the inversion symmetry of the qubit and induce both the parametrically enhanced transverse and longitudinal couplings to the resonators, resulting in strong nonlinear two-photon interactions between the qubit and the resonators and enabling the scheme to be implemented in a relatively weak coupling regime. With an additional microwave drive applied to the qubit, the dissipation of the qubit used as a resource can help drive the resonators into the desired superpositions of squeezed coherent states at a steady state with high speed. Numerical simulations show that the target states with high fidelity and highly nonlinear properties can be created for a long time even in the presence of photon leakage out of the resonators. The scheme can be generalized to other quantum platforms and may have potential applications in the field of quantum information processing and the improvement of estimation precision in quantum metrology.
We propose a fast scheme to generate Schr\"odinger cat states in a superconducting resonator using a continuously driven qubit without resorting to the dispersive regime, two-photon drives, or engineered two-photon dissipation. We provide analysis for when the qubit is on and off resonance from the drive. We extend our analysis to account for a third level in a weakly anharmonic qutrit. We also discuss the case of a strongly anharmonic qutrit. Throughout the paper, we corroborate our analytical results with numerical simulations in the presence of energy relaxation and dephasing of the qubit and resonator using realistic experimental parameters.
We study a superconducting circuit that can act as a toolbox to generate various Bogoliubov linear and nonlinear quantum operations on the microwave photon modes of superconducting resonators within one single circuit. The quantum operations are generated by exploring dispersive four-wave mixing (FWM) processes involving the resonator modes. Different FWM geometries can be realized by adjusting the circuit parameters and by applying appropriate microwave drivings. We illustrate this scheme using a circuit made of two superconducting qubits that couple with each other. Each qubit couples with one superconducting resonator. We also discuss main sources of quantum errors in this system and study the fidelity of the quantum operations by numerical simulation. Our scheme provides a practical approach to realize quantum information protocols on superconducting resonators.