Context Mixing via Ground State Search

To address context mixing problem via ground state search, we introduce an effective Hamiltonian whose ground state presents the best mixing of a prior given probability distributions to approximately describe unknown target probability distribution.Comment: 5 pages; Some errors in v1 were correcte

Annealing Approach to Quantum Tomography

Annealing approach to quantum tomography is theoretically proposed. First, based on the maximum entropy principle, we introduce classical parameters to combine "quantum models (or quantum states)" given a prior for potentially representing the unknown target state. Then, we formulate the quantum tomography as an optimization problem on the classical parameters, by employing relative entropy of the parametrized state with the target state as the objective function to be minimized. We show that the objective function is physically implementable, in a theoretical sense at least, as an effective Hamiltonian to be induced by physical interactions of the system with environment systems being prepared in the target state. Corollary, applying quantum annealing to the effective Hamiltonian, we can execute quantum tomography by obtaining the ground state that gives the optimal parameters.Comment: 11 pages, 4 figure

Dynamical detailed balance and local KMS condition for non-equilibrium states

The principle of detailed balance is at the basis of equilibrium physics and is equivalent to the Kubo-Martin-Schwinger (KMS) condition (under quite general assumptions). In the present paper we prove that a large class of open quantum systems satisfies a dynamical generalization of the detailed balance condition ({\it dynamical detailed balance}) expressing the fact that all the micro-currents, associated to the Bohr frequencies are constant. The usual (equilibrium) detailed balance condition is characterized by the property that this constant is identically zero. From this we deduce a simple and experimentally measurable relation expressing the microcurrent associated to a transition between two levels $\epsilon_m\to\epsilon_n$ as a linear combination of the occupation probabilities of the two levels, with coefficients given by the generalized susceptivities (transport coefficients). Finally, using a master equation characterization of the dynamical detailed balance condition, we show that this condition is equivalent to a "local" generalization of the usual KMS condition.Comment: REVTex4, 23page

Annealing Dynamics via Quantum Interference of Forward and Backward Time Evolved States

Toward an alternative approach to the quantum mechanic ground state search, we theoretically introduce a protocol in which energy of two identical systems are deterministically exchanged. The protocol utilizes a quantum interference between "forward" and "backward" time evolved states with respect to a given Hamiltonian. In addition, to make use the protocol for the ground state search, we construct a network with which we may be able to efficiently apply the protocol successively among multiple systems so that energy of one of them is gradually approaching the lowest one. Although rigorous analysis on the validity of the network is left as a future challenge, some properties of the network are also investigated.Comment: 11 pages, 6 figures. Revised protocol in section 2, results unchanged. Corrected typo

Quantum Annealing Mechanism as A Measurement Process

An idea for an application of the quantum annealing mechanism to construct a projection measurement in a collective space is proposed. We use the annealing mechanism to drive the pointer degree of freedom associated with the measurement process. The parameters in its problem Hamiltonian is given not as classical variables but as quantum variables (states). By additionally introducing successive short interactions so that the back reaction to the quantum state (to be measured) can be controlled, we invent a quantum mechanically parametrized quantum annealing process. Applying to a particular problem of discrimination of two collective states , we find that the process by the quantum mechanically parametrized annealing arrives at projection measurement in the collective space when the parametrizing quantum variables themselves are orthogonal (or distinguishable).Comment: 7 pages, 5 figure

Stochastic limit approximation for rapidly decaying systems

The stochastic limit approximation method for ``rapid'' decay is presented, where the damping rate \gamma is comparable to the system frequency \Omega, i.e., \gamma \sim \Omega, whereas the usual stochastic limit approximation is applied only to the weak damping situation \gamma << \Omega. The key formulas for rapid decay are very similar to those for weak damping, but the dynamics is quite different. From a microscopic Hamiltonian, the spin-boson model, a Bloch equation containing two independent time scales is derived. This is a useful method to extract the minimal dissipative dynamics at high temperature kT >> \hbar\Omega and the master equations obtained are of the Lindblad form even for the Caldeira-Leggett model. The validity of the method is confirmed by comparing the master equation derived through this method with the exact one.Comment: REVTeX, 6 pages; To be published in Phys. Rev. A 63 (Feb. 2000

On the physical meaning of the EPR--chameleon experiment

The physical meaning of the EPR--chameleon experiment proposed in AcRe00b,AcRe01a, in which the EPR correlations are reproduced by local, independent, deterministic choices is re-examined. In addition we extend the mathematical model of AcRe00b,AcRe01a by showing that the dynamics considered there is effectively the reduced dynamics of a fully reversible evolution. We also propose a new protocol, more directly corresponding to real experiments, in which the local computers only send back to the central one the results of the evaluation of $\pm1$--valued functions. The program to run the experiment is available from the WEB-page: http://volterra.mat.uniroma2.it

Effects of Inelastic Scattering on Tunneling Time in Generalized Nelson's Quantum Mechanics

We analyze the effects of inelastic scattering on the tunneling time theoretically, using generalized Nelson's quantum mechanics. This generalization enables us to describe quantum system with optical potential and channel couplings in a real time stochastic approach, which seems to give us a new insight into quantum mechanics beyond Copenhagen interpretation.Comment: 25 pages, 10 Postscript figure

How much security does Y-00 protocol provide us ?

New quantum cryptography, often called Y-00 protocol, has much higher performance than the conventional quantum cryptographies. It seems that the conventional quantum cryptographic attacks are inefficient at Y-00 protocol as its security is based on the different grounds from that of the conventional ones. We have, then, tried to cryptoanalyze Y-00 protocol in the view of cryptographic communication system. As a result, it turns out that the security of Y-00 protocol is equivalent to that of classical stream cipher.Comment: 4 pages, 4 figure

Toward Practical-Scale Quantum Annealing Machine for Prime Factoring

We propose a prime factorizer operated in a framework of quantum annealing (QA). The idea is inverse operation of a multiplier implemented with QA-based Boolean logic circuits. We designed the QA machine on an application-specific-annealing-computing architecture which efficiently increases available hardware budgets at the cost of restricted functionality. The invertible operation of QA logic gates consisting of superconducting flux qubits was confirmed by circuit simulation with classical noise sources. The circuits were implemented and fabricated by using superconducting integrated circuit technologies with Nb/AlOx/Nb Josephson junctions. We also propose a 2.5Dimensional packaging scheme of a qubit-chip/interpose /package-substrate structure for realizing practically large-scale QA systems.Comment: 17 pages, 11 figure