Coherent control and charge echo in a GaAs charge qubit

In fulfilling the non-adiabatic requirement of pulse sequences, it is challenging to perform multi-pulse quantum control of a charge qubit. By optimizing our charge qubit and pulse parameters, we experimentally demonstrate the coherent control and echo process of a GaAs charge qubit. We firstly employed a single non-adiabatic voltage pulse to perform the Larmor oscillation experiment and determine the optimal ${\sigma }_x$ operation pulses. Then, we produced Ramsey fringes using two ${\sigma }_x=\pi /2$ pulses and extracted the decoherence time $T_2^{\ast }\sim 112\text{ps}$ from the Ramsey fringes. More importantly, we successfully applied a charge echo pulse sequence to increase the extracted inhomogeneous dephasing time to ∼1360 ps. Our results show that the low-frequency noise is the important dephasing limiter of the coherence time of the charge qubit in the GaAs system. (letter)