Kyu-Hwang Yeon

Quantum squeezing effect of mesoscopic capacitance–inductance–resistance coupled circuit

Abstract Quantum fluctuations and squeezing effect of charges and currents of mesoscopic capacitance–inductance–resistance coupled circuit are investigated using canonical transformation and unitary transformation method. Even if the resistance of the mesoscopic circuit is zero, the uncertainty relation between charges and those conjugate currents do not satisfy minimum uncertainty relation. We confirmed that the uncertainties of charge can be reduced by paying the cost that the uncertainties of currents becoming larger relatively, or vice versa.

Quantum uncertainties of mesoscopic capacitance coupled circuit

Abstract The quantum invariant operator and unitary transformation operator of mesoscopic capacitance coupled circuit are obtained. The uncertainty relation of the charges and the currents are calculated. The uncertainty relations between charges and currents do not satisfy minimum uncertainty relation, ( Δq i Δp i ) min =ℏ/2, even though resistances R 1 and R 2 are zero.

Deterministic controlled-phase gate and preparation of cluster states via singly charged quantum dots in cavity quantum electrodynamics

A controlled-phase gate is constructed deterministically in a quantum dot (QD)-cavity system based on Faraday rotation via singly charged QDs in the strong-coupling regime. The fidelity of the gate can reach relatively high values even if cavity decay and leakage are considered. Furthermore, we present two schemes for implementing N-qubit cluster states for electron spins and photons, respectively, by exploiting this gate. The schemes are very simple and can be easily realized in the current experiment.

One-step implementation of a multiqubit controlled-phase gate with superconducting quantum interference devices coupled to a resonator

A scheme for one-step implementation of an n-qubit controlled-phase gate is proposed in a superconducting quantum interference device (SQUID) system. The distinguishing feature of this scheme is the simultaneous and nonidentical off-resonant Raman coupling of the n SQUID qubits to a single-mode resonator and the microwave pulses. The scheme is efficient and simple because it requires only one-step evolution, and no adjustments of the experimental parameters are needed during the operation.

Preparation of multipartite entangled states and one-step implementation of 1?M economical phase-covariant quantum anti-cloning in cavity QED

The scheme for preparing a multipartite entangled state and implementing 1→M economical phase-covariant quantum anti-cloning only by one step are proposed. By using the symmetric and asymmetric interactions between N atoms and the cavity, N-particle Greenberger–Horne–Zeilinger (GHZ) and W states are prepared, respectively. Furthermore, a scheme of 1→M anti-cloning is also proposed through preparing the W state. The decoherence from atomic spontaneous emission is negligible due to the excited state of the atom being adiabatically eliminated under large detuning. The scheme is insensitive to the cavity decay due to the cavity only being virtually excited. The experimental feasibility of the present scheme is also discussed.

Generation of a three-dimensional N-atom GHZ state based on optical-fiber-connected cavity quantum electrodynamics

A scheme for the generation of a three-dimensional N-atom GHZ state is proposed by combining some two-qubit swap operations and single-qubit rotation operations. The swap operation can easily be achieved by the large-detuned coupling of two distant atoms to two optical-fiber-connected cavities, respectively driven by two classical fields, and the single-bit rotation operation can be obtained by the interaction of an atom with a classical field. During the generation processes, atomic spontaneous emission and cavity decay are negligible. The scheme is realizable in experiments with current cavity quantum electrodynamics techniques.

Optimal universal and phase-covariant quantum cloning machines with quantum-dot spins in cavity QED

Schemes for implementing a 1 ? 2 optimal universal quantum cloning machine (UQCM) and a 1 ? 3 ancilla-free optimal phase-covariant quantum cloning machine (PCCM) are proposed by manipulating the transverse spin?spin interactions of quantum dots mediated by a vacuum single-mode cavity. The interactions among different quantum dots are selectively controlled by the classical laser fields. These quantum cloning machines are more robust due to the very long spin decoherence time of quantum dots. Furthermore, the experimental implementation is simplified in comparison with those using atoms as qubits. The quantum dots are embedded in the cavity simultaneously; hence the troubles caused by the qubits passing through multiple cavities are effectively avoided.

Realization of optimal symmetric universal and phase-covariant quantum cloning with quantum dot spins in cavity QED

We present a scheme to implement a special quantum cloning machine with quantum dot spins in cavity QED. The quantum cloning machine copies the information from a photon to other two distant quantum dots trapped in cavities with the help of a single-photon pulse. Choosing the different parameters, the scheme can implement optimal symmetric 1 → 2 universal, optimal symmetric 1 → 2 phase-covariant and optimal symmetric economical 1 → 3 phase-covariant quantum cloning machines. The present scheme is more economical in saving resource compared with previous schemes.

Physical realization of a multi-purpose quantum cloning machine with electron spins in quantum dots

We propose a scheme to realize a quantum cloning machine via coupled electron spins in quantum dots. By properly designing the position of the quantum dots and controlling the coupling between them, a multi-purpose quantum cloning machine (MPCM) including an optimal symmetric (asymmetric) 1→2 universal quantum cloning machine (UQCM) and optimal symmetric (asymmetric) 1→2 phase-covariant quantum cloning machine (PCCM) can be achieved.

Implementing 1 → M economical phase-covariant cloning and telecloning in cavity QED

We propose a scheme to implement 1 → M economical phase-covariant quantum cloning by using N three-level atoms nonresonantly interacting with a cavity assisted by a classical laser field. Using this interaction 1 → M telecloning is also implemented by applying the maximal entangled W state and partial entangled W state as the quantum channel, respectively. It is pointed out by analysing the fidelities and success probabilities that a relatively high fidelity and success probability can be obtained by choosing an appropriate channel in terms of the pre-known information of the input state.