Showing papers by "Myungshik Kim published in 2009"
TL;DR: It is shown that Dicke states have interesting applications in multiparty quantum networking protocols such as open-destination teleportation, telecloning, and quantum secret sharing.
Abstract: We report the first experimental generation and characterization of a six-photon Dicke state. The produced state shows a fidelity of $F=0.56\ifmmode\pm\else\textpm\fi{}0.02$ with respect to an ideal Dicke state and violates a witness detecting genuine six-qubit entanglement by 4 standard deviations. We confirm characteristic Dicke properties of our resource and demonstrate its versatility by projecting out four- and five-photon Dicke states, as well as four-photon Greenberger-Horne-Zeilinger and $W$ states. We also show that Dicke states have interesting applications in multiparty quantum networking protocols such as open-destination teleportation, telecloning, and quantum secret sharing.
228 citations
TL;DR: This work presents the experimental realization of a scheme, based on single-photon interference, for implementing superpositions of distinct quantum operations and provides a direct and quantitative verification of the bosonic commutation relation between creation and annihilation operators.
Abstract: We present the experimental realization of a scheme, based on single-photon interference, for implementing superpositions of distinct quantum operations. Its application to a thermal light field (a well-categorized classical entity) illustrates quantum superposition from a new standpoint and provides a direct and quantitative verification of the bosonic commutation relation between creation and annihilation operators. By shifting the focus towards operator superpositions, this result opens interesting alternative perspectives for manipulating quantum states.
126 citations
TL;DR: In this article, the authors propose a scheme for determining the coupling parameters in a chain of interacting spins using only time-resolved measurements over a single particle, simple data postprocessing and no state initialization or prior knowledge of the state of the chain.
Abstract: We propose a scheme for the determination of the coupling parameters in a chain of interacting spins. This requires only time-resolved measurements over a single particle, simple data postprocessing and no state initialization or prior knowledge of the state of the chain. The protocol fits well into the context of quantum-dynamics characterization and is efficient even when the spin chain is affected by general dissipative and dephasing channels. We illustrate the performance of the scheme by analyzing explicit examples and discuss possible extensions.
73 citations
TL;DR: In this article, the dynamics of an array of coupled optical cavities, each containing an ensemble of qubits, were analyzed, and it was shown that the nonlinearity inherent in the dynamics inherent in each ensemble coupled to the respective cavity field allows the formation of solitons.
Abstract: In view of current research effort on semiconducting photonic-crystal defect microcavities, we consider the dynamics of an array of coupled optical cavities, each containing an ensemble of qubits. By concentrating on the strong coupling regime, we analytically prove that the nonlinearity inherent in the dynamics of each ensemble coupled to the respective cavity field allows the formation of solitons. We further show how the use of the Holstein–Primakoff transformation and the large-detuning limit with the cavity allows one to recover the Bose–Hubbard model.
23 citations
TL;DR: In this paper, the authors introduce three compact graph states that can be used to perform a measurement-based Toffoli gate, and they show that success probabilities of $1∕4, $ 1∕2, and 1, respectively, can be achieved.
Abstract: We introduce three compact graph states that can be used to perform a measurement-based Toffoli gate. Given a weighted graph of six, seven, or eight qubits, we show that success probabilities of $1∕4$, $1∕2$, and 1, respectively, can be achieved. Our study puts a measurement-based version of this important quantum logic gate within the reach of current experiments. As the graphs are setup independent, they could be realized in a variety of systems, including linear optics and ion traps.
11 citations
TL;DR: In this paper, it was shown that Gaussian states with the same variance are the only states which bring about factorizable output fields, while it is normal that two independent input fields are superposed at the beam splitter to give correlated outputs.
Abstract: A beam splitter is one of the most important devices in an optics laboratory because of its handiness and versatility; equivalent devices are found in various quantum systems to couple two subsystems or to interfere them. While it is normal that two independent input fields are superposed at the beam splitter to give correlated outputs, identical Gaussian states interfere there to produce totally independent output fields. We prove that Gaussian states with same the variance are the only states which bring about factorizable output fields.
9 citations
TL;DR: In this paper, the authors adopt the well-accepted definition of nonclassicality in the form of lack of well-defined positive Glauber-Sudarshan $P$ function describing the state.
Abstract: Continuous-variable entanglement is a manifestation of nonclassicality of quantum states. In this paper, we attempt to analyze whether and under which conditions nonclassicality can be used as an entanglement criterion. We adopt the well-accepted definition of nonclassicality in the form of lack of well-defined positive Glauber-Sudarshan $P$ function describing the state. After demonstrating that the classicality of subsystems is not sufficient for the nonclassicality of the overall state to be identifiable with entanglement, we focus on Gaussian states and find specific local unitary transformations required to arrive at this equivalency. This is followed by the analysis of quantitative relation between nonclassicality and entanglement.
7 citations
TL;DR: It is shown that two separated parties, performing only phase space measurements on a composite quantum system with a positive Wigner function and performing only operationally local transformations that preserve this positivity, can nonetheless violate Bell's inequality.
Abstract: Bell conjectured that a positive Wigner function does not allow violation of the inequalities imposed by local hidden variable theories. A requirement for this conjecture is "when phase space measurements are performed." We introduce the theory-independent concept of "operationally local transformations" which refers to the change of the switch on a local measurement apparatus. We show that two separated parties, performing only phase space measurements on a composite quantum system with a positive Wigner function and performing only operationally local transformations that preserve this positivity, can nonetheless violate Bell's inequality. Such operationally local transformations are realized using entangled ancillae.
5 citations
TL;DR: A quantum state is teleported between two atoms that are 1 meter apart through their entanglement with photons.
Abstract: A quantum state is teleported between two atoms that are 1 meter apart through their entanglement with photons
3 citations
TL;DR: In this article, the authors consider two separated oscillators initially in equilibrium and continuously interacting with thermal environments and propose a way to entangle them using a mediating qubit, which removes the necessity of fine-tuning interaction times, and results in a high tolerance of the entanglement to finite temperature.
Abstract: We consider two separated oscillators initially in equilibrium and continuously interacting with thermal environments and propose a way to entangle them using a mediating qubit. An appropriate interaction allows for an analytic treatment of the open system, removes the necessity of fine-tuning interaction times, and results in a high tolerance of the entanglement to finite temperature. The entanglement thus produced between the oscillators can be verified either through a Bell inequality relying on oscillator parity measurements or through conditional extraction of the entanglement on two mutually noninteracting qubits. The latter process also shows that the generated mixed-entangled state of the oscillators is an useful resource for entangling qubits. By allowing for influences from environments, taking feasible qubit-oscillator interactions and measurement settings, this scheme should be implementable in a variety of experimental setups. The method presented for the solution of the master equation can also be adapted to a variety of problems involving the same form of qubit-oscillator interaction
2 citations
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TL;DR: In this article, an energy relaxation mechanism was proposed for strongly correlated spin systems to decay into their ground states, driven by cavity quantum electrodynamics interaction and the decay of cavity photons.
Abstract: We propose an energy relaxation mechanism whereby strongly correlated spin systems decay into their ground states. The relaxation is driven by cavity quantum electrodynamics interaction and the decay of cavity photons. It is shown that by applying broadband driving fields, strongly correlated systems can be cooled regardless of the specific details of their energy level profile. The scheme would also have significant implications in other contexts, such as adiabatic quantum computation and steady-state entanglement in dissipative systems.