Qubit coherent control with squeezed light fields

Quantum control fields that operate on a qubit in a single quantum gatemay become entangled with the qubit and thus contribute to the gate error. We have investigated the possible advantage of the use of squeezed light forqubit coherent control and compared it with the more standard coherent lightcontrol field. We have calculated the entanglement between a short pulse ofresonant squeezed light and a two-level atom in free space during the ¼ pulseoperation on a qubit and the resulting operational error.

We found that for squeezed light, the interplay of three phases – the squeezing-phase, thephase of the light field and the atomic phase related to the superpositionof qubit levels, determine the error and the entanglement magnitude. Incomparison with the coherent control using coherent light, the error and theentanglement can be either enhanced or suppressed depending on the abovephase relations.

We have discussed the possibility to measure the increasedgate error as a signature of this entanglement.