Quantum Uctuations Research Articles

Generation and Detection of Squeezed Phonon

The variance of the time dependent atomic positions and momenta is directly mapped into the quantum uctuations of the photon number of the scattered probing light. A fully quantum de-scription of the non-linear interactions between photonic and phononic fields unveils evidences of squeezing of thermal phonons. In here a pump-probe spectroscopy was proposed to observe phonon squeezing in solids. Numerical simulation showed pump-probe response due to coherent phonon and squeezed phonon in alpha-quartz.

Superuid-Mott glass quantum multicritical point on a percolating lattice

We employ large-scale Monte Carlo simulations to study a particle-hole symmetric site-diluted quantum rotor model in two dimensions. The ground state phase diagram of this system features two distinct quantum phase transitions between the superuid and the insulating (Mott glass) phases. They are separated by a multicritical point. The generic transition for dilutions below the lattice percolation threshold is driven by quantum uctuations while thetransition across the percolation threshold is due to the geometric uctuations of the lattice. We determine the location of the multicritical point between these two transitions and find its critical behavior. The multicritical exponents read z = 1:72(2), β/ν = 0:41(2), and γ/ν = 2:90(5). We compare our results to other quantum phase transitions in disordered systems, and we discuss experiments.

On the possibility of using optical y-splitter in quantum random number generation systems based on fluctuations of vacuum

current on detectors after beam splitting. We derived equations allowing one to estimate the scheme parameters imperfection impact on measurement results. We also obtained mathematical expressions, demonstrating the equivalence of quantum description of Y-splitter and beam splitter with two inputs, which allows the use Y-splitter for the implementation of quantum random number generation systems based on vacuum quantum uctuations.

To What Extent the Superfluid <sup>4</sup>He is Squeezed?

We show that the Bogoliubov microscopic theory of superuidity of liquid 4 He allows quantum uctuations of both condensate and excitations. Comparison of those uctuations leads to an equation determining the mean number of atoms with zero momentum in a self-consistent way. Obtained results are in good agreement with the experiments on Bose-Einstein condensation in atomic beams. To explain experimental results on low amount of atoms in condensate in the superuid phase of liquid 4 He, we propose to consider the ground state of the condensate as a squeezed number state and discuss some corollaries coming from this conjecture.

Frenkel-Kontorova Model: Crossover from the Classical to the Quantum Mechanical

The Frenkel-Kontorova (FK) model describes a chain of atoms connected by springs subject to an external potential. This simple classical model exhibits a wealth of complex behavior. It has also found applications in many condensed matter systems such as charge density waves, magnetic spirals, modulated phases and tribology. However, an in-depth understanding of some of these problems, for example, tribology in the nano-regime, demands an understanding of its quantum mechanical behavior. To achieve this goal, we use a squeezed-state approach rst used in quantum optics. We found that quantum uctuations renormalize the standard map, which governs the classical behavior of the FK model, to a sawtooth map. This result is borne out by Monte-Carlo simulations. We also found that the ground state wave function changes from an extended state to a localized state when the coupling constant increases. Although quantum uctuations largely smear the transition by breaking of analyticity observed in the classical case, the remnant of this transition is still discernible.