Superconducting quantum bit reading device

Abstract

The invention provides a superconducting quantum bit reading device, which comprises a quantum bit, a reading cavity and a Josephson junction, and is characterized in that the quantum bit and the reading cavity are coupled through the Josephson junction. According to the invention, the longitudinal coupling (ZZ coupling) of the bit and the reading cavity is realized, and the driving error of the transverse coupling (XX coupling) to the quantum bit during reading in the prior art is reduced, so that the reading fidelity can be improved by improving the reading power in the application.

Description

technical field [0001] The invention relates to the field of quantum computing, in particular to a reading device for superconducting qubits. Background technique [0002] The dispersion measurement of the superconducting qubit refers to coupling the subbit to be measured with a linear resonant cavity, so that the state of the bit will change the frequency of the resonant cavity. In this way, we can indirectly measure the state of the bit by measuring the frequency of the resonant cavity. [0003] The key to dispersion measurement is to couple the qubits to the read cavity. In the prior art, the superconducting qubit and the resonant cavity are usually coupled through capacitance. The effect produced by this coupling structure is the transverse coupling in quantum mechanics, or XX coupling. Its Hamiltonian can be written as follows: [0004] [0005] where ω r is the frequency of the read cavity, ω q is the transition frequency of the bit, and g is the coupling stre...

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Problems solved by technology

[0008] In the process of realizing the concept of the present invention, the inventors have found that there are at least the following problems in the related art: the bit-read cavity coupling form adopted in the above method is essentially a transverse coupling, and only under the approximate premise of large detuning Taking the energy eigenstate basis vector of the cavity as a whole is shown as longitudinal coupling

Therefore, when the read signal is strong and the number of photons in the read cavity is large, the bit will be driven by the read cavity and cause measurement errors

Therefore, the strength of the read signal is limited in the prior art

Limits on read signal strength translate directly into limits on read fidelity given the presence of noise in the read signal

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