Abstract
The latest technological progress of achieving the ultrastrong-coupling regime in circuit quantum electrodynamics (QED) systems has greatly promoted the developments of quantum physics, where novel quantum optics phenomena and potential computational benefits have been predicted. Here, we propose a scheme to accelerate the nontrivial two-qubit phase gate in a circuit QED system, where superconducting flux qubits are ultrastrongly coupled to a transmission line resonator (TLR), and two more TLRs are coupled to the ultrastrongly-coupled system for assistant. The nontrivial unconventional geometric phase gate between the two flux qubits is achieved based on close-loop displacements of the three-mode intracavity fields. Moreover, as there are three resonators contributing to the phase accumulation, the requirement of the coupling strength to realize the two-qubit gate can be reduced. Further reduction in the coupling strength to achieve a specific controlled-phase gate can be realized by adding more auxiliary resonators to the ultrastrongly-coupled system through superconducting quantum interference devices. We also present a study of our scheme with realistic parameters considering imperfect controls and noisy environment. Our scheme possesses the merits of ultrafastness and noise-tolerance due to the advantages of geometric phases.
Highlights
Quantum computing has attracted much attention due to its acknowledged potential in solving hard problems over its classical counterparts, such as prime factoring, database searching, and etc
We explore an ultrastrongly coupled qubit-resonator system involving flux qubits galvanically connected to a transmission line resonator (TLR), which is linked to another two empty resonators by superconducting quantum interference devices
We propose the use of ancillary microwave resonators as a tool to further accelerate the protected quantum computation in the ultrastrong coupling regime
Summary
Quantum computing has attracted much attention due to its acknowledged potential in solving hard problems over its classical counterparts, such as prime factoring, database searching, and etc. Superconducting circuit systems are promising platforms for quantum computation and quantum simulation because of its exotic properties such as scalability, controllability, flexibility, and compatibility with micro-fabrication[1]. Considerable progresses have been made in recent superconducting circuit experiments involving the observation of the dynamical Casimir effects[10], the realization of adiabatic quantum gate operations[11], the demonstration of digital quantum simulation[12], and so on. Geometric quantum computation has been experimentally implemented in various quantum systems such as thermal ensembles of molecules[32], solid-state spins[33], superconducting qubits[34] and so on. We explore an ultrastrongly coupled qubit-resonator system involving flux qubits galvanically connected to a transmission line resonator (TLR), which is linked to another two empty resonators by superconducting quantum interference devices. Since there are three resonators contributing to the phase accumulation, it is possible to largely relax the requirement of very large coupling strength needed to achieve the phase gate as compared to the gate proposal in ref
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