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Masahiro Hotta

Publications and source records attributed to Masahiro Hotta.

49 records · Page 3Linked to original sources
arXiv2010

Energy-Entanglement Relation for Quantum Energy Teleportation

Protocols of quantum energy teleportation (QET), while retaining causality and local energy conservation, enable the transportation of energy from a subsystem of a many-body quantum system to a distant subsystem by local operations and classical communication through ground-state entanglement. We prove two energy-entanglement inequalities for a minimal QET model. These relations help us to gain a profound understanding of entanglement itself as a physical resource by relating entanglement to energy as an evident physical resource.

quant-ph↗
arXiv2010

Controlled Hawking Process by Quantum Energy Teleportation

In this paper, a new quantum mechanical method to extract energy from black holes with contracting horizons is proposed. The method is based on a gedanken experiment on quantum energy teleportation (QET), which has been recently proposed in quantum information theory. We consider this QET protocol for N massless fields in near-horizon regions of large-mass black holes with near-horizon geometry described by the Minkowski metric. For each field, a two-level spin is strongly coupled with the local quantum fluctuation outside the horizon during a short time period. After the measurement of N fields, N-bit information is obtained. During the measurement, positive-energy wave packets of the fields form and then fall into the black hole. The amount of excitation energy is independent of the measurement result. After absorption of the wave packets and increase of the black hole mass, a measurement-result-dependent local operation of the N fields is performed outside the horizon. Then, accompanying the extraction of positive energy from the quantum fluctuation by the operation, negative-energy wave packets of the fields form and then fall into the black hole, decreasing the black hole mass. This implies that a part of the absorbed positive energy emitted from the measurement devices is effectively retrieved from the black hole via the measurement results.

gr-qc↗
arXiv2010

Quantum Energy Teleportation with Electromagnetic Field: Discrete vs. Continuous Variables

It is well known that usual quantum teleportation protocols cannot transport energy. Recently, new protocols called quantum energy teleportation (QET) have been proposed, which transport energy by local operations and classical communication with the ground states of many-body quantum systems. In this paper, we compare two different QET protocols for transporting energy with electromagnetic field. In the first protocol, a 1/2 spin (a qubit) is coupled with the quantum fluctuation in the vacuum state and measured in order to obtain one-bit information about the fluctuation for the teleportation. In the second protocol, a harmonic oscillator is coupled with the fluctuation and measured in order to obtain continuous-variable information about the fluctuation. In the spin protocol, the amount of teleported energy is suppressed by an exponential damping factor when the amount of input energy increases. This suppression factor becomes power damping in the case of the harmonic oscillator protocol. Therefore, it is concluded that obtaining more information about the quantum fluctuation leads to teleporting more energy. This result suggests a profound relationship between energy and quantum information.

quant-ph↗
arXiv2009

Ground-State Entanglement gives birth to Quantum Energy Teleportation

Ground-state entanglement induces emergence of negative-energy-density regions in quantum systems by squeezing zero-point oscillation, keeping total energy of the systems nonnegative. By use of the negativity of quantum energy density, protocols of quantum energy teleportation are proposed that transport energy to distant sites by local operations and classical communication. The energy is teleported without breaking any physical laws including causality and local energy conservation. Because intermediate subsystems of the energy transfer channel are not excited during the protocol execution, the protocol attains energy transportation without heat generation in the channel. We discuss the protocol focusing around qubit chains. In addition, we address a related problem of breaking ground-state entanglement by measurements.

quant-ph↗
arXiv2009

Quantum Energy Teleportation with Trapped Ions

We analyse a protocol of quantum energy teleportation that transports energy from the left edge of a linear ion crystal to the right edge by local operations and classical communication at a speed considerably greater than the speed of a phonon in the crystal. A probe qubit is strongly coupled with phonon fluctuation in the ground state for a short time, and it is projectively measured in order to obtain information about this phonon fluctuation. During the measurement process, phonons are excited by the time-dependent measurement interaction, and the energy of the excited phonons must be infused from outside the system. The obtained information is transferred to the right edge of the crystal through a classical channel. Even though the phonons excited at the left edge do not arrive at the right edge at the same time as when the information arrives at the right edge, we are able to soon extract energy from the ions at the right edge by using the transferred information. Because the intermediate ions of the crystal are not excited during the execution of the protocol, energy is transmitted in the energy transfer channel without heat generation.

quant-ph↗
arXiv2008

Quantum Energy Teleportation in Spin Chain Systems

We propose a protocol for quantum energy teleportation which transports energy in spin chains to distant sites only by local operations and classical communication. By utilizing ground-state entanglement and notion of negative energy density region, energy is teleported without breaking any physical laws including causality and local energy conservation. Because not excited physical entity but classical information is transported in the protocol, the dissipation rate of energy in transport is expected to be strongly suppressed.

quant-ph↗
arXiv2008

Quantum Measurement Information as a key to Energy Release from Local Vacuums

In this paper, a protocol is proposed in which energy extraction from local vacuum states is possible by using quantum measurement information for the vacuum state of quantum fields. In the protocol, Alice, who stays at a spatial point, excites the ground state of the fields by a local measurement. Consequently, wavepackects generated by A' measurement propagate the vacuum to spatial infinity. Let us assume that Bob stays away from Alice and fails to catch the excitation energy when the wavepackets pass in front of him. Next Alice announces her local measurement result to Bob by classical communication. Bob performs a local unitary operation depending on the measurement result. In this process, positive energy is released from the fields to Bob's apparatus of the unitary operation. In the field systems, wavepackets are generated with negative energy around Bob's location. Soon afterwards, the negative -energy wavepackets begin to chase after the positive-energy wavepackets generated by Alice and form loosely bound states.

gr-qc↗
arXiv2008

A Protocol for Quantum Energy Distribution

A new protocol, quantum energy distribution (QED), is proposed in which multiple parties can simultaneously extract positive energy from spin chains by common secret keys shared by an energy supplier. QED is robust against impersonation; an adversary, who does not have a common secret key and attempts to get energy, will instead give energy to the spin chains. The total amount of energy transfer gives a lower bound of the residual energy of any local cooling process by the energy supplier.

quant-ph↗
arXiv2008

Secure Quantum Passwords

We propose a quantum authentication protocol that is robust against the theft of secret keys. In the protocol, disposable quantum passwords prevent impersonation attacks with stolen secret keys. The protocol also prevents the leakage of secret information of a certification agent.

quant-ph↗
arXiv2008

A Fundamental Lower Bound of Actuating Energy for Broadband Photon Switching

We derive a universal lower bound of actuating energy $E_{s}$ for broadband photon switching by using an uncertainty relation between time and the negative energy density of quantum fields. We find that broadband photon switching between perfect reflection and perfect transmission over a time $t_s$ should satisfy $E_{s}\geq\frac{\hbar}{6πt_s}$.

quant-ph↗
arXiv2008

Channel Estimation Theory of Low-Noise Multiple Parameters:Attainablity Problem of the Cram{é}r-Rao Bounds

For decoherence processes induced by weak interactions with the environment, a general quantum channel with one noise parameter has been formulated. This channel is called low-noise channel and very useful for investigating the parameter estimation in the leading order. In this paper, we formulate the low-noise channel with multiple unknown parameters in order to address the simultaneous achievability of the Cram{é}r-Rao bound for the parameters estimation. In general, the simultaneous achievement of the Cram{é}r-Rao bound for multi-parameter estimations suffers from non-commutativity of optimal measurements for respective parameters. However, with certain exceptions, we show that the Cram{é}r-Rao bound for output states of dissipative low-noise channels can be always attained in the first order of the parameters as long as D \leq N-1, where D and N denote the number of the parameters and the dimension of the system, respectively. This condition is replaced by D \leq N^{2}-1 if it is allowed to set the entanglement with ancilla systems in its input state and to perform the non-local measurement on the composite system.

quant-ph↗
arXiv2005

Ancilla-Assisted Enhancement of Channel Estimation for Low-Noise Parameters

In order to make a unified treatment for estimation problems of a very small noise or a very weak signal in a quantum process, we introduce the notion of a low-noise quantum channel with one noise parameter. It is known in several examples that prior entanglement together with nonlocal output measurement improves the performance of the channel estimation. In this paper, we study this ``ancilla-assisted enhancement'' for estimation of the noise parameter in a general low-noise channel. For channels on two level systems we prove that the enhancement factor, the ratio of the Fisher information of the ancilla-assisted estimation to that of the original one, is always upper bounded by 3/2. Some conditions for the attainability are also given with illustrative examples.

quant-ph↗