# All

We provide a study of various quantum phase transitions occurring in the XY

Heisenberg chain in a transverse magnetic field using the Meyer-Wallach (MW)

measure of (global) entanglement. Such a measure, while being readily

evaluated, is a multipartite measure of entanglement as opposed to more

commonly used bipartite measures. Consequently, we obtain analytic expression

of the measure for finite-size systems and show that it can be used to obtain

critical exponents via finite-size scaling with great accuracy for the Ising

Hereunder we continue the study of the representation theory of the algebra

of permutation operators acting on the $n$-fold tensor product space, partially

transposed on the last subsystem. We develop the concept of partially reduced

irreducible representations, which allows to simplify significantly previously

proved theorems and what is the most important derive new results for

irreducible representations of the mentioned algebra. In our analysis we are

Collinear antiferromagnets (AFs) support two degenerate magnon excitations

carrying opposite spin polarizations, by which magnons can function as

electrons in spin transport. We explore the interlayer coupling mediated by

antiferromagnetic magnons in an insulating ferromagnet (F)/AF/F trilayer

structure. The internal energy of the AF depends on the orientations of the two

Fs, which manifests as effective interlayer interactions JS1.S2 and K(S1.S2)^2.

Both J and K are functions of temperature and the AF thickness. Interestingly,

We demonstrate a Bayesian quantum game on an ion trap quantum computer with

five qubits. The players share an entangled pair of qubits and perform

rotations on their qubit as the strategy choice. Two five-qubit circuits are

sufficient to run all 16 possible strategy choice sets in a game with four

possible strategies. The data are then parsed into player types randomly in

order to combine them classically into a Bayesian framework. We exhaustively

compute the possible strategies of the game so that the experimental data can

An extension of the input-output relation for a conventional Michelson

interferometric gravitational-wave detector is carried out to treat an

arbitrary coherent state for the injected optical beam. This extension is one

of necessary researches toward the clarification of the relation between

conventional gravitational-wave detectors and a simple model of a

gravitational-wave detector inspired by weak-measurements in [A.~Nishizawa,

Phys. Rev. A {\bf 92} (2015), 032123.]. The derived input-output relation

We study the "anti-Unruh effect" for an entangled quantum state in reference

to the counterintuitive cooling previously pointed out for an accelerated

detector coupled to the vacuum. We show that quantum entanglement for an

initially entangled (spacelike separated) bipartite state can be increased when

either a detector attached to one particle is accelerated or both detectors

attached to the two particles are in simultaneous accelerations. However, if

Bloch oscillations in a single Josephson junction in the phase-slip regime

relate current to frequency. They can be measured by applying a periodic drive

to a DC-biased, small Josephson junction. Phase-locking between the periodic

drive and the Bloch oscillations then gives rise to steps at constant current

in the I-V curves, also known as dual Shapiro steps. Unlike conventional

Shapiro steps, a measurement of these dual Shapiro steps is impeded by the

presence of a parasitic capacitance. This capacitance shunts the junction

We explore ways to use the ability to measure the populations of individual

magnetic sublevels to improve the sensitivity of magnetic field measurements

and measurements of atomic electric dipole moments (EDMs). When atoms are

initialized in the $m=0$ magnetic sublevel, the shot-noise-limited uncertainty

of these measurements is $1/\sqrt{2F(F+1)}$ smaller than that of a Larmor

precession measurement. When the populations in the even (or odd) magnetic

sublevels are combined, we show that these measurements are independent of the

We propose a simple architecture for a scalable quantum network, in which the

quantum nodes consist of qubit systems confined in cavities. The nodes are

deterministically coupled by transmission and reflection of photons, which are

disentangled from the qubits at the end of each operation. A single photon can

generate an entangling controlled phase (C-PHASE) gate between any selected

number of qubits in the network and forms the basis for universal quantum

A double-slit experiment with entangled photons is theoretically analyzed. It

is shown that, under suitable conditions, two entangled photons of wavelength

$\lambda$ can behave like a \emph{biphoton} of wavelength $\lambda/2$. The

interference of these biphotons, passing through a double-slit can be obtained

by detecting both photons of the pair at the same position. This is in

agreement with the results of an earlier experiment. More interestingly, we