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 $\Delta$ and ${\bar \Delta}$. 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 $\Delta$, ${\bar \Delta}$, ${\tilde e}^c$ (anti-slepton), even if the triplet Higgs mass $M_\Delta$ is much larger than the gravitino mass $m_{3/2} \sim 10^3 {\rm GeV}$. Specifically, due to the effects of the potential terms provided with the superpotential terms $M_\Delta {\bar \Delta} \Delta$, $(\lambda_{L /} / 2M) {\bar \Delta} {\bar \Delta} e^c e^c$, $(\lambda_\Delta / 2M) {\bar \Delta} \Delta {\bar \Delta} \Delta$ ($\lambda_{L /} / \lambda_\Delta \sim 0.3 - 3$), the phases of $\Delta$, ${\bar \Delta}$, ${\tilde e}^c$ are rotated at the time with the Hubble parameter $H \sim M_\Delta$, producing generally the asymmetry with fraction $\epsilon_L \sim 0.1$. If $M_\Delta$ 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