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Minimal Energy Cost to Initialize a Quantum Bit with Tolerable Error

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 $\mathcal{L}^{2}(ε)/τ$ from the Landaeur's limit ($k_{B}T\ln2$) for a finite-time $τ$ initialization with an error probability $ε$. The thermodynamic length $\mathcal{L}(ε)$ between the states before and after initializing in the parametric space increases monotonously as the error decreases. For example, in the constant dissipation coefficient ($γ_{0}$) case, the minimal additional cost is $0.997k_{B}T/(γ_{0}τ)$ for $ε=1\%$ and $1.288k_{B}T/(γ_{0}τ)$ for $ε=0.1\%$. 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.