Minimal Energy Cost to Initialize a Quantum Bit with Tolerable Error

Abstract

Landauer's principle imposes a fundamental limit on the energy cost to perfectly initialize a classical bit, which is only reached under the ideal operation with infinite-long time. The question on the cost in the practical operation for a quantum bit (qubit) has been posted under the constraint by the finiteness of operation time. We discover a raise-up of energy cost by $\mathcal{L}^{2}(\epsilon)/\tau$ from the Landaeur's limit ($k_{B}T\ln2$) for a finite-time $\tau$ initialization with an error probability $\epsilon$. The thermodynamic length $\mathcal{L}(\epsilon)$ between the states before and after initializing in the parametric space increases monotonously as the error decreases. For example, in the constant dissipation coefficient ($\gamma_{0}$) case, the minimal additional cost is $0.997k_{B}T/(\gamma_{0}\tau)$ for $\epsilon=1\%$ and $1.288k_{B}T/(\gamma_{0}\tau)$ for $\epsilon=0.1\%$. Furthermore, the optimal protocol to reach the bound of minimal energy cost is proposed for the qubit initialization realized via a finite-time isothermal process.