Efficient protocol for qubit initialization with a tunable environment
journal contributionposted on 05.09.2017, 11:03 by Jani Tuorila, Matti Partanen, Tapio Ala-NissilaTapio Ala-Nissila, Mikko Mottonen
We propose an efficient qubit initialization protocol based on a dissipative environment that can be dynamically adjusted. Here, the qubit is coupled to a thermal bath through a tunable harmonic oscillator. On-demand initialization is achieved by sweeping the oscillator rapidly into resonance with the qubit. This resonant coupling with the engineered environment induces fast relaxation to the ground state of the system, and a consecutive rapid sweep back to off resonance guarantees weak excess dissipation during quantum computations. We solve the corresponding quantum dynamics using a Markovian master equation for the reduced density operator of the qubit-bath system. This allows us to optimize the parameters and the initialization protocol for the qubit. Our analytical calculations show that the ground-state occupation of our system is well protected during the fast sweeps of the environmental coupling and, consequently, we obtain an estimate for the duration of our protocol by solving the transition rates between the low-energy eigenstates with the Jacobian diagonalization method. Our results suggest that the current experimental state of the art for the initialization speed of superconducting qubits at a given fidelity can be considerably improved.
This work was supported by the Academy of Finland through its Centers of Excellence Programme under grant numbers 251748 and 284621, and through grant number 305306. We also acknowledge funding from the European Research Council under Consolidator Grant number 681311 (QUESS) and from the Vilho, Yrjo, and Kalle Vaisala Foundation.
- Mathematical Sciences