arXiv subjects

Shi Biao Zheng

Publications and source records attributed to Shi Biao Zheng.

3 recordsLinked to original sources

arXiv2012

Simplified construction of $n$-qubit controlled phase gates and physical realization

We show that with the assistance of a third level of the qubits an n-qubit phase gate can be constructed from $2n-4$ two-qutrit conditional swap gates, a single qutrit-qubit controlled phase gate, and two single-qutrit operations. Unlike previous schemes, our scheme uses the auxiliary level to "expose" some state to the qutrit-qubit controlled phase gate, instead of using it to "hide" states from the conditional dynamics. Neither the number of the additional levels nor that of single-qutrit operations needs to increase with $n$. We propose a physical implementation of the required elementary gates in cavity QED, and show that the total gate time may be greatly reduced as compared with that required in the previous methods.

quant-ph↗

arXiv2012

Generation of atomic and field squeezing by adiabatic passage and symmetry breaking

We propose an efficient scheme for realizing squeezing for both an atomic ensemble and a cavity field via adiabatic evolution of the dark state of the atom-cavity system. Controlled symmetry breaking of the Hamiltonian ensures a unique dark state for the total system, in which the atomic system or cavity mode is squeezed depending upon the choice of the detunings. Since the generation of the atomic squeezed state requires neither the cavity mode nor the atomic system to be excited, the decoherence effects are effectively suppressed. The scheme is insensitive to the uncertainty in the atomic number and imperfect timing, and the time needed for the generation of the desired squeezed state decreases as the size of the system grows. The required experimental techniques are within the scope of what can be obtained in the present cavity QED setups.

quant-ph↗

arXiv2012

Cooling distant atoms into entangled states via coupled cavities

We propose a scheme for generating steady entanglement between two distant atomic qubits in the coupled-cavity system via laser cooling. With suitable choice of the laser frequencies, the target entangled state is the only ground state that is not excited by the lasers due to large detunings. The laser excitations of other ground states, together with dissipative processes, drive the system to the target state which is the unique steady state of the system. Numerical simulation shows that the maximally entangled state with high fidelity can be produced with presently available cooperativity.

quant-ph↗