Section: New Results

Dynamically protected cat-qubits: a new paradigm for universal quantum computation

Participant : Mazyar Mirrahimi.

In a close collaboration with the teams of Michel Devoret, Robert Schoelkopf and Liang Jiang (Department of Applied Physics, Yale university) and in particular a former member of our group, Zaki Leghtas, we have presented a new hardware-efficient paradigm for universal quantum computation. This paradigm is based on encoding, protecting and manipulating quantum information in a quantum harmonic oscillator. This proposal exploits multi-photon driven dissipative processes to encode quantum information in logical bases composed of Schrödinger cat states. More precisely, we consider two schemes. In a first scheme, a two-photon driven dissipative process is used to stabilize a logical qubit basis of two-component Schrödinger cat states. While such a scheme ensures a protection of the logical qubit against the photon dephasing errors, the prominent error channel of single-photon loss induces bit-flip type errors that cannot be corrected. Therefore, we have considered a second scheme based on a four-photon driven dissipative process which leads to the choice of four-component Schrödinger cat states as the logical qubit. Such a logical qubit can be protected against single-photon loss by continuous photon number parity measurements. Next, applying some specific Hamiltonians, we have provided a set of universal quantum gates on the encoded qubits of each of the two schemes. In particular, we have illustrated how these operations can be rendered fault-tolerant with respect to various decoherence channels of participating quantum systems. Finally, we have also proposed experimental schemes based on quantum superconducting circuits and inspired by methods used in Josephson parametric amplification, which should allow to achieve these driven dissipative processes along with the Hamiltonians ensuring the universal operations in an efficient manner.

This proposal was published in New Journal of Physics [12] and has also been chosen by the editor as an IOPselect paper for the novelty, significance and potential impact on future research.