Generation of an N -qubit phase gate via atom–cavity nonidentical coupling

A scheme for approximate generation of an N-qubit phase gate is proposed in cavity QED based on nonidentical coupling between the atoms and the cavity.The atoms interact with a highly detuned cavity-field mode,but quantum information does not transfer between the atoms and cavity field,and thus the cavity decay is negligible.The gate time does not rise with an increase in the number of qubits.With the choice of a smaller odd number l (related to atom–cavity coupling constants),the phase gate can be generated with a higher fidelity and a higher success probability in a shorter time (the gate time is much shorter than the atomic radiative lifetime and photon lifetime).When the number of qubits N exceeds certain small values,the fidelity and success probability rise slowly with an increase in the number of qubits N.When N →∞,the fidelity and success probability infinitely approach 1,but never exceed 1.