arXiv subjects

Riuji Mochizuki

Publications and source records attributed to Riuji Mochizuki.

16 recordsLinked to original sources

arXiv2019

Decoherence as an inherent characteristic of quantum mechanics

We show that it is possible to explain the quantum measurement process within the framework of quantum mechanics without any additional postulates. The key concept of the theory is decoherence, which appears as an inherent characteristic of quantum mechanics and results from the uncertainty relation. In contrast to environment-induced decoherence, this decoherence exists prior to a measurement being made. To clarify our idea, we examine three elemental experiments: a Stern-Gerlach-like experiment, the Einstein-Podolsky-Rosen-Bohm (EPR-Bohm) experiment, and the double-slit experiment. By considering the first experiment, we explain how the uncertainty relation between position and momentum introduces decoherence prior to measurement. Consideration of the EPR-Bohm experiment leads us to conclude that the correlation of the EPR pair is not a consequence of what is known as the collapse of the wave function. Our theory of decoherence can also be applied to experiments with continuous eigenvalues, such as the double-slit experiment. Consideration of the double-slit experiment leads us to understand how pure quantum mechanics describes the fact that quanta behave as interfering particles.

physics.gen-ph↗

arXiv2019

Non-unitary Process and Quantum Communication

The no-communication theorem states that the observation of a subsystem of an entangled state does not affect another subsystem. Nevertheless, this theorem is based on the assumption that all quantum processes are unitary. We examine a feasible thought experiment and show that a non-unitary process included in this thought experiment enables the transmission of information by means of the quantum observation process.

physics.gen-ph↗

arXiv2019

Quantum communication by means of collapse of the wave function

We show that quantum communication by means of collapse of the wave function is possible. In this study, quantum communication does not mean quantum teleportation or quantum cryptography, but transmission of information itself. Because of consistency with special relativity, the possibility of the quantum communication leads to another conclusion that the collapse of the wave function must propagate at the speed of light or slower. We show this requirement is consistent with nonlocality in quantum mechanics. We also demonstrate that the Einstein-Podolsky-Rosen experiment does not disprove our conclusion.

physics.gen-ph↗

arXiv2018

Understanding weak values without new probability theory

The physical meaning of weak values and measurements can be completely understood with Born rule and the general probability theory. It is known that the weak value of an observable $\hat A$ with post-selection $\langle F|$ may be out of the eigenvalue range of $\hat A$. This is because the weak value of $\hat A$ with the post-selection is, in general, not the expectation value of $\hat A$, but the expectation value of $\hat A| F\rangle\langle F|$ boosted by the post-selection.

quant-ph↗

arXiv2016

Nonseparability and simultaneous readability

In this study, we investigate quantum nonseparability between an observed system and a measuring apparatus, or multiple measuring apparatuses. We show that the physical meaning of the outcome of the measuring apparatus obtained by weak measurement with a post-selection differs critically from that without any post-selection. In this study, the nonseparability plays the essential role, which is shown to be the same in a simultaneous conventional von Neumann-type measurement of multiple observables. From this viewpoint, we suggest a new concept, known as {\it simultaneous readability}, which is the possibility that multiple measuring apparatuses will give the proper information of the observed system simultaneously. Next, we show that different components of the spin of an electron are not simultaneously measurable even if it has EPR correlation with another electron.

quant-ph↗

arXiv2014

Weak value as an indicator of back-action

In this study we critically examine some important papers on weak measurement and weak values. We find some insufficiency and mistakes in these papers, and we demonstrate that the real parts of weak values provide the back-action to the post-selection, which is caused by weak measurement. Two examples, a counterfactual statement of Hardy's paradox and experiments that determine the average trajectory of photons passing through double slits, are investigated from our view point.

quant-ph↗

arXiv2013

T-duality and dimensional reduction of S-brane solutions

We studied dimensional reduction and T-duality in spacelike brane solutions of 10 or 11 dimensional supergravity, including spacelike counterparts of wave and monopole solutions. Dimensional reduction is well-defined if, and only if, the solutions possess static dimensions. However, T-duality is ill-defined for some of these solutions where dilaton expectation values depend on time. This led us to conclude that supergravity solutions should be regarded as low-energy solutions of superstring theory only if dilaton expectation values are independent of time.

hep-th↗

arXiv2013

Quantum logic and weak values

In this study, we study weak values from a quantum-logical viewpoint. In addition, we examine the validity of the counterfactual statements of Hardy's paradox, which are based on weak values, and we show that these statements have not been validated. It is also shown that strange weak values may only appear if they are not (conditional) probabilities. PACS numbers: 03.65.Ta, 03.65.Ud, 03.65.Ca

quant-ph↗

arXiv2012

Simultaneous measurability of error and disturbance

The uncertainty relation, which displays an elementary property of quantum theory, was originally described by Heisenberg as the relation between error and disturbance. Ozawa presented a more rigorous expression of the uncertainty relation, which was later verified experimentally. Nevertheless, the operators corresponding to error and disturbance should be measurable in the identical state if we follow the presupposition of Heisenberg's thought experiment. In this letter, we discuss simultaneous measurability of error and disturbance and present a new inequality using error and disturbance in the identical state. A testable example of this inequality is also suggested.

quant-ph↗

arXiv2012

Stability of S-brane singular solutions and expansion of the universe

We investigate stability of single S-brane singular solutions obtained in our previous papers. A stable perturbative solution exists for each of them, while an unstable one exists only if the dilaton field does not depend on time. We apply these perturbative solutions to inflation and late-time acceleration of expansion of the universe.

hep-th↗

arXiv2011

A necessary condition for brane solutions to have their origins in string field theory

We present a necessary condition for brane solutions to have their origins in string field theory. For such solutions, T-duality operations between IIA and IIB solutions should be well-defined. Nevertheless, not all S-brane solutions have T-duality. The solutions that have T-duality and may accordingly be regarded as low-energy solutions of string field theory satisfy a condition in which some S-brane distributions are forbidden.

hep-th↗

arXiv2007

Eternally inflating cosmologies from intersecting spacelike branes

Intersecting spacelike braneworld cosmologies are investigated. The time axis is set on the scale parameter of extra space, which may include more than one timelike metric. Obtained are eternally inflating (i.e. undergoing late-time inflation) Robertson-Walker spacetime and extra space with a constant scale factor. In the case of multibrane solutions, some dimensions are static or shrink. The fact that the largest supersymmetry algebra contains 32 supercharges in 4 dimensions imposes a restriction on the geometry of extra space.

hep-th↗

arXiv2006

Eternally accelerating spacelike braneworld cosmologies

We construct an eternally inflating spacelike brane world model. If the space dimension of the brane is three (SM2) or six (SM5) for M theory or four (SD3) for superstring theory, a time-dependent $n$-form field would supply a constant energy density and cause exponentially expansion of the spacelike brane. In these cases, the hyperbolic space perpendicular to the brane would not vary in size. In the other cases, however, the extra space would vary in size.

hep-th↗

arXiv1999

Energy Conservation and the Unruh Effect

In this paper it is explicitly demonstrated that the energy conservation law is kept when a detector uniformly accelerated in the Minkowski vacuum is excited and emits a particle. This fact had been hidden in conventional approaches in which detectors were considered to be forced on trajectories. To lift the veil we suggest a detector model written in terms of the Minkowski coordinates. In this model the Hamiltonian of the detector involves a classical potential term instead of the detector's fixed trajectory. The transition rate agrees with the corresponding conventional one in the limit of an infinite mass detector though even then the recoil remains.

gr-qc↗

arXiv1998

Back Reaction to Rotating Detector

It has been a puzzle that rotating detector may respond even in the appropriate vacuum defined via canonical quantization. We solve this puzzle by taking back reaction of the detector into account. The influence of the back reaction, even in the detector's mass infinite limit, appears in the response function. It makes the detector possible to respond in the vacuum if the detector is rotating, though the detector in linear uniform motion never respond in the vacuum as expected from Poincare invariance.

hep-th↗

arXiv1997

Energy Radiation from a Moving Mirror with Finite Mass

In this paper we study energy radiation from a moving mirror in 1+1 dimensional space-time. The mirror is assumed to have finite mass and accordingly to receive back reaction from scalar photon field. The mode expansion of the scalar field becomes different from that without back reaction though the trajectory of the mirror is not changed. Then energy density of the vacuum becomes to have finite value proportional to square of the mass of the mirror. Moreover we compute the energy momentum tensor of the radiation in the case that acceleration of the mirror is small. As a result we show that the mirror creates energy radiation whose quantity does not depend on its mass but on its acceleration even if the acceleration is uniform.

hep-th↗