Controlled decoherence of floating flux qubits

In Born--Markov approximation, this paper calculates the energy relaxation time T₁ and the decoherence time T₂ of a floating flux qubit by solving the set of Bloch--Redfield equations. It shows that there are two main factors influencing the floating flux qubits: coupling capacitor in the circuit and the environment resistor. It also discusses how to improve the quantum coherence time of a qubit. Through shunt connecting/ series connecting inductive elements, an inductive environment resistor is obtained and further the reactance component of the environment resistor is improved,which is beneficial to the enhancement of decoherence time of floating flux qubits.