109 research outputs found
Optical homodyne detection in view of joint probability distribution
Optical homodyne detection is examined in view of joint probability
distribution. It is usually discussed that the relative phase between
independent laser fields are localized by photon-number measurements in
interference experiments such as homodyne detection. This provides reasoning to
use operationally coherent states for laser fields in the description of
homodyne detection and optical quantum-state tomography. Here, we elucidate
these situations by considering the joint probability distribution and the
invariance of homodyne detection under the phase transformation of optical
fields.Comment: 8 pages, 2 figures; REVTeX 4.
Cluster-based architecture for fault-tolerant quantum computation
We present a detailed description of an architecture for fault-tolerant
quantum computation, which is based on the cluster model of encoded qubits. In
this cluster-based architecture, concatenated computation is implemented in a
quite different way from the usual circuit-based architecture where physical
gates are recursively replaced by logical gates with error-correction gadgets.
Instead, some relevant cluster states, say fundamental clusters, are
recursively constructed through verification and postselection in advance for
the higher-level one-way computation, which namely provides error-precorrection
of gate operations. A suitable code such as the Steane seven-qubit code is
adopted for transversal operations. This concatenated construction of verified
fundamental clusters has a simple transversal structure of logical errors, and
achieves a high noise threshold ~ 3 % for computation by using appropriate
verification procedures. Since the postselection is localized within each
fundamental cluster with the help of deterministic bare controlled-Z gates
without verification, divergence of resources is restrained, which reconciles
postselection with scalability.Comment: 16 pages, 34 figure
Affleck-Dine leptogenesis with triplet Higgs
We study an extension of the supersymmetric standard model including a pair
of electroweak triplet Higgs and . The neutrinos
acquire Majorana masses mediated by these triplet Higgs fields rather than the
right-handed neutrinos. The successful leptogenesis for baryogenesis can be
realized after the inflation through the Affleck-Dine mechanism on a flat
manifold consisting of , ,
(anti-slepton), even if the triplet Higgs mass is much larger than
the gravitino mass . Specifically, due to the
effects of the potential terms provided with the superpotential terms , ,
(), the phases of , , are rotated at the time with the Hubble parameter , producing generally the asymmetry with fraction . If is large enough, this early leptogenesis can be
completed before the thermal effects take place.Comment: 11 pages, 2 figure
Photon creation in a resonant cavity with a nonstationary plasma mirror and its detection with Rydberg atoms
We investigate the dynamical Casimir effect and its detection with Rydberg
atoms. The photons are created in a resonant cavity with a plasma mirror of a
semiconductor slab which is irradiated by periodic laser pulses. The canonical
Hamiltonian is derived for the creation and annihilation operators showing the
explicit time-variation in the couplings, which originates from the external
configuration such as a nonstationary plasma mirror. The number of created
photons is evaluated as squeezing from the Heisenberg equations with the
Hamiltonian. Then, the detection of the photons as the atomic excitations is
examined through the atom-field interaction. Some consideration is made for a
feasible experimental realization with a semiconductor plasma mirror.Comment: 8 pages, 2 figure
Leptogenesis with supersymmetric Higgs triplets in TeV region
The leptogenesis with supersymmetric Higgs triplets is studied in the light
of experimental verification in the TeV region. The lepton number asymmetry
appears just after the inflation via multiscalar coherent evolution of Higgs
triplets and antislepton on a flat manifold. If the Higgs triplet mass terms
dominate over the negative thermal-log term for the Hubble parameter H
comparable to the Higgs triplet mass M_\Delta, the asymmetry is fixed readily
to some significant value by the redshift and rotation of these scalar fields,
providing the sufficient lepton-to-entropy ratio n_L / s \sim 10^-10. This can
be the case even with M_\Delta \sim 1 TeV for the reheating temperature T_R
\sim 10^6 GeV and the mass parameter M / \lambda \sim 10^22 GeV of the
nonrenormalizable superpotential terms relevant for leptogenesis.Comment: 8 Pages, 2 figures. The discussion about the stability of the VEV's
of the Higgs triplets is adde
Anti-Zeno Effect for Quantum Transport in Disordered Systems
We demonstrate that repeated measurements in disordered systems can induce
quantum anti-Zeno effect under certain condition to enhance quantum transport.
The enhancement of energy transfer is really exhibited with a simple model
under repeated measurements. The optimal measurement interval for the anti-Zeno
effect and the maximal efficiency of energy transfer are specified in terms of
the relevant physical parameters. Since the environment acts as frequent
measurements on the system, the decoherence-induced energy transfer, which has
been discussed recently for photosynthetic complexes, may be interpreted in
terms of the anti-Zeno effect. We further find an interesting phenomenon, where
local decoherence or repeated measurements may even promote entanglement
generation between the non-local sites.Comment: 5pages, 3 figures; v2: published versio
Analysis for practical realization of number-state manipulation by number-sum Bell measurement with linear optics
We analyze the linear optical realization of number-sum Bell measurement and
number-state manipulation by taking into account the realistic experimental
situation, specifically imperfectness of single-photon detector. The present
scheme for number-state manipulation is based on the number-sum Bell
measurement, which is implemented with linear optical elements, i.e., beam
splitters, phase shifters and zero-one-photon detectors. Squeezed vacuum states
and coherent states are used as optical sources. The linear optical Bell state
detector is formulated quantum theoretically with a probability operator
measure. Then, the fidelity of manipulation and preparation of number-states,
particularly for qubits and qutrits, is evaluated in terms of the quantum
efficiency and dark count of single-photon detector. It is found that a high
fidelity is achievable with small enough squeezing parameters and coherent
state amplitudes.Comment: 13 pages, 9 figure
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