Browsing by Author "Chen, Yueh-Nan"

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Current induced entanglement of double quantum dot excitons
(2003)
Chen, Yueh-Nan
;
Chuu, Der-San
;
電子物理學系
;
Department of Electrophysics
We propose to measure Purcell effect by observing the current through a semeiconductor quantum dot embedded inside a microcavity. The stationary current is shown to be altered if one varies the cavity length. For the double-dot system, we find that the stationary current shows oscillatory behavior as one varies the inter-dot distance. Furthermore, the current is suppressed if the dot distance is small compared to the wavelength of the emitted photon. This photon trapping phenomenon generates the entangled state and may be used to control the emission of single photons at predetermined times.
Detecting non-Markovian plasmonic band gaps in quantum dots using electron transport
(2009-06-01)
Chen, Yueh-Nan
;
Chen, Guang-Yin
;
Liao, Ying-Yen
;
Lambert, Neill
;
Nori, Franco
Placing a quantum dot close to a metal nanowire leads to drastic changes in its radiative decay behavior because of evanescent couplings to surface plasmons. We show how two non-Markovian effects, band edge and retardation, could be observed in such a system. Combined with a quantum-dot p-i-n junction, these effects could be readout via current-noise measurements. We also discuss how these effects can occur in similar systems with restricted geometries, such as phononic cavities and photonic crystal waveguides. This work links two previously separate topics: surface plasmons and current-noise measurements.
Entanglement detection via the condition of quantum correlation
(2007-09-01)
Li, Che-Ming
;
Hsu, Li-Yi
;
Chen, Yueh-Nan
;
Chuu, Der-San
;
Brandes, Tobias
We develop a necessary condition of quantum correlation. It is utilized to construct a d-level bipartite Bell-type inequality which is strongly resistant to noise and requires only analyses of O(d) measurement outcomes compared to the previous result O(d(2)). Remarkably, a connection between the arbitrary high-dimensional bipartite Bell-type inequality and entanglement witnesses is found. Through the necessary condition of quantum correlation, we propose that the witness operators to detect truly multipartite entanglement for a generalized Greenberger-Horne-Zeilinger (GHZ) state with two local measurement settings and a four-qubit singlet state with three settings. Moreover, we also propose a robust entanglement witness to detect a four-level tripartite GHZ state with only two local measurement settings.
Experimental violation of Bell inequalities for multi-dimensional systems
(2016-02-26)
Lo, Hsin-Pin
;
Li, Che-Ming
;
Yabushita, Atsushi
;
Chen, Yueh-Nan
;
Luo, Chih-Wei
Quantum correlations between spatially separated parts of a d-dimensional bipartite system (d >= 2) have no classical analog. Such correlations, also called entanglements, are not only conceptually important, but also have a profound impact on information science. In theory the violation of Bell inequalities based on local realistic theories for d-dimensional systems provides evidence of quantum nonlocality. Experimental verification is required to confirm whether a quantum system of extremely large dimension can possess this feature, however it has never been performed for large dimension. Here, we report that Bell inequalities are experimentally violated for bipartite quantum systems of dimensionality d=16 with the usual ensembles of polarization-entangled photon pairs. We also estimate that our entanglement source violates Bell inequalities for extremely high dimensionality of d>4000. The designed scenario offers a possible new method to investigate the entanglement of multipartite systems of large dimensionality and their application in quantum information processing.
Proposal for detection of non-Markovian decay via current noise
(2008-01-01)
Chen, Yueh-Nan
;
Chen, Guang-Yin
;
物理研究所
;
Institute of Physics
We propose to detect non-Markovian decay of an exciton qubit coupled to multimode bosonic reservoir via shot-noise measurements. Nonequilibrium current noise is calculated for a quantum dot embedded inside a p-i-n junction. An additional term from non-Markovian effect is obtained in the derivation of noise spectrum. As examples, two practical photonic reservoirs, photon vacuum with the inclusion of cut-off frequency and surface plasmons, are given to show that the noise may become super-Poissonian due to this non-Markovian effect. Utilizing the property of super-radiance is further suggested to enhance the noise value.
Quantifying the nonclassicality of pure dephasing
(2019-08-22)
Chen, Hong-Bin
;
Lo, Ping-Yuan
;
Gneiting, Clemens
;
Bae, Joonwoo
;
Chen, Yueh-Nan
One of the central problems in quantum theory is to characterize, detect, and quantify quantumness in terms of classical strategies. Dephasing processes, caused by non-dissipative information exchange between quantum systems and environments, provides a natural platform for this purpose, as they control the quantum-to-classical transition. Recently, it has been shown that dephasing dynamics itself can exhibit (non)classical traits, depending on the nature of the system-environment correlations and the related (im)possibility to simulate these dynamics with Hamiltonian ensembles-the classical strategy. Here we establish the framework of detecting and quantifying the nonclassicality for pure dephasing dynamics. The uniqueness of the canonical representation of Hamiltonian ensembles is shown, and a constructive method to determine the latter is presented. We illustrate our method for qubit, qutrit, and qubit-pair pure dephasing and describe how to implement our approach with quantum process tomography experiments. Our work is readily applicable to present-day quantum experiments.
Simulating Open Quantum Systems with Hamiltonian Ensembles and the Nonclassicality of the Dynamics
(2018-01-19)
Chen, Hong-Bin
;
Gneiting, Clemens
;
Lo, Ping-Yuan
;
Chen, Yueh-Nan
;
Nori, Franco
The incoherent dynamical properties of open quantum systems are generically attributed to an ongoing correlation between the system and its environment. Here, we propose a novel way to assess the nature of these system-environment correlations by examining the system dynamics alone. Our approach is based on the possibility or impossibility to simulate open-system dynamics with Hamiltonian ensembles. As we show, such (im) possibility to simulate is closely linked to the system-environment correlations. We thus define the nonclassicality of open-system dynamics in terms of the nonexistence of a Hamiltonian-ensemble simulation. This classifies any nonunital open-system dynamics as nonclassical. We give examples for open-system dynamics that are unital and classical, as well as unital and nonclassical.
Spontaneous emission of quantum dot excitons into surface plasmons in a nanowire
(2008-10-01)
Chen, Guang-Yin
;
Chen, Yueh-Nan
;
Chun, Der-San
;
電子物理學系
;
物理研究所
The spontaneous emission (SE) of quantum dot (QD) excitons into surface plasmons in a cylindrical nanowire is investigated theoretically. Maxwell's equations with appropriate boundary conditions are solved numerically to obtain the dispersion relations of surface plasmons. The SE rate of QD excitons is found to be greatly enhanced at certain values of the exciton bandgap. Application in generation of remote entangled states via superradiance is also pointed out and may be observable with current technology. (C) 2008 Optical Society of America
Study of fluorescence enhancement of colloidal CdSe/ZnS quantum dots bound to hexadecylamine by single-molecule measurements
(2007-10-25)
Yuan, Chi-Tsu
;
Chou, Wu-Ching
;
Chen, Yueh-Nan
;
Chou, Jui-Wen
;
Chuuji, Der-San
Fluorescence enhancement of colloidal CdSe/ZnS quantum dots (QDs) by the binding of hexadecylamine (HDA) ligands was investigated at the single-QD level. The blinking behavior of individual CdSe/ZnS QDs can be dramatically modified by additional HDA ligands. Both the ratio of the mean on/off time lengths and the total number of emitted photons within the on-time duration can be enhanced, by factors of up to 2.8 and 13, respectively. Consequently, the blinking rate can be suppressed down to 18%. The fluorescence decay curve is closer to a single-exponential decay profile and has a longer measured lifetime. These results suggest that HDA ligands can further improve surface passivation.