## Physics

### Strong quadrature squeezing and quantum amplification in a coupled Bose-Einstein condensate- optomechanical cavity via coherent modulation. (arXiv:1807.10324v2 [quant-ph] UPDATED)

arXiv.org: Quantum Physics - Sun, 2018-11-04 18:33

We consider an optomechanical cavity with a movable end-mirror as a quantum mechanical oscillator (MO) containing an interacting cigar-shaped Bose-Eisenstein condensate (BEC). It is assumed that both the MO and the BEC interact with the radiation pressure of the cavity field in the red-detuned and weak coupling regimes while the two-body atomic collisions frequency of the BEC and the mechanical spring coefficient of the MO are coherently modulated. By analyzing the scattering matrix we find that a frequency-dependent squeezing is induced to the three subsystems only due to the coherent modulations. In the largely different cooperativities regime together with strong modulations, the mechanical mode of the MO and the Bogoliubov mode of the BEC exhibit quadrature squeezing which can surpass the so-called 3dB limit (up to 75 dB) with high robustness to the thermal noises. Surprisingly, in this regime by controlling the system and modulation parameters, a very high degree of squeezing (up to 16 dB) together with high purity of quantum state for the output cavity field is achievable. Furthermore, one can attain simultaneous strong quantum amplification, added-noise suppression, and controllable gain-bandwidth for the complementary quadratures of squeezed ones in the subsystems.

Categories: Journals, Physics

### Monitoring Decoherence via Measurement of Quantum Coherence. (arXiv:1807.05021v3 [quant-ph] UPDATED)

arXiv.org: Quantum Physics - Sun, 2018-11-04 18:33

A multi-slit interference experiment, with which-way detectors, in the presence of environment induced decoherence, is theoretically analyzed. The effect of environment is modeled via a coupling to a bath of harmonic oscillators. Through an exact analysis, an expression for $\mathcal{C}$, a recently introduced measure of coherence, of the particle at the detecting screen is obtained as a function of the parameters of the environment. It is argued that the effect of decoherence can be quantified using the measured coherence value which lies between zero and one. For the specific case of two slits, it is shown that the decoherence time can be obtained from the measured value of the coherence, $\mathcal{C}$, thus providing a novel way to quantify the effect of decoherence via direct measurement of quantum coherence. This would be of significant value in many current studies that seek to exploit quantum superpositions for quantum information applications and scalable quantum computation.

Categories: Journals, Physics

### Quantum Metrology in the Kerr Metric. (arXiv:1810.13119v1 [gr-qc] CROSS LISTED)

arXiv.org: Quantum Physics - Sun, 2018-11-04 18:33

A surprising feature of the Kerr metric is the anisotropy of the speed of light. The angular momentum of a rotating massive object causes co- and counter-propagating light paths to move at faster and slower velocities, respectively. Based on this effect we derive ultimate quantum limits for the measurement of the Kerr rotation parameter $a$ using a interferometric set up. As a possible implementation, we propose a Mach-Zender interferometer to measure the "one-way height differential time effect". We isolate the effect by calibrating to a dark port and rotating the interferometer such that only the direction dependent Kerr phase term remains. We also identify a flat metric where the observers see $c = 1$. We use this metric and the Lorentz transformations to calculate the same Kerr phase shift. We then consider non-stationary observers moving with Earth$'$s rotation, and find an additional phase from the classical relative motion.

Categories: Journals, Physics

### Quantum-enhanced correlated interferometry for fundamental physics tests. (arXiv:1810.13386v2 [quant-ph] UPDATED)

arXiv.org: Quantum Physics - Sun, 2018-11-04 18:33

Improvements in measurement precision have historically led to new scientific discoveries, with gravitational wave detection being a recent prime example. The research field of quantum metrology deals with improving the resolution of instruments that are otherwise limited by quantum shot-noise. Quantum metrology is therefore a promising avenue for enabling scientific breakthroughs. Here we present the first feasibility tests of quantum-enhanced correlated interferometry, which outperforms the sensitivity of a single interferometer in revealing faint stochastic noise by several orders of magnitude. Using quantum-enhanced correlation techniques we detected an injected signal, invisible to the single interferometer, reaching a sensitivity of $3\times10^{-17}m/\sqrt{Hz}$ ($1/20$ of the shot-noise) at $13.5 MHz$ in a few seconds of integration time. By injecting bipartite quantum correlated states into the interferometers we also demonstrated a noise reduction in the subtraction of the interferometer outputs. The experimental techniques employed here could potentially be applied to solve open questions in fundamental physics, such as the detection of the stochastic gravitational wave background or primordial black holes, or to test the predictions of particular Planck scale theories.

Categories: Journals, Physics

### Topological Quantum Optics in Two-dimensional Photonic Crystals. (arXiv:1810.12299v2 [quant-ph] UPDATED)

arXiv.org: Quantum Physics - Sun, 2018-11-04 18:33

We propose a nanophotonic quantum optical platform that gives rise to two-dimensional topological bands at optical frequencies with large band gaps. Our system is composed of a two-dimensional lattice of non-linear quantum emitters embedded in a photonic crystal slab. The emitters interact through the guided modes of the photonic crystal, and a uniform magnetic field gives rise to a topological band structure with a band that is almost completely flat. Topological edge states arise on the boundaries of the system that are robust to missing lattice sites and to the inhomogeneous broadening of emitters. These results pave the way for exploring topological many-body states in quantum optical systems.

Categories: Journals, Physics

### Uniform stationary measure of space-inhomogeneous quantum walks in one dimension. (arXiv:1810.12504v2 [quant-ph] UPDATED)

arXiv.org: Quantum Physics - Sun, 2018-11-04 18:33

The discrete-time quantum walk (QW) is a quantum version of the random walk (RW) and has been widely investigated for the last two decades. Some remarkable properties of QW are well known. For example, QW has a ballistic spreading, i.e., QW is quadratically faster than RW. For some cases, localization occurs: a walker stays at the starting position forever. In this paper, we consider stationary measures of two-state QWs on the line. It was shown that for any space-homogeneous model, the uniform measure becomes the stationary measure. However, the corresponding result for space-inhomogeneous model is not known. Here, we present a class of space-inhomogeneous QWs on the line and cycles in which the uniform measure is stationary. Furthermore, we briefly discuss a difference between QWs and RWs.

Categories: Journals, Physics

### Casimir Thrust Force on a Rotating Chiral Particle. (arXiv:1810.08366v3 [quant-ph] UPDATED)

arXiv.org: Quantum Physics - Sun, 2018-11-04 18:33

In the work, the thermal and vacuum fluctuation is predicted capable of generating a Casimir thrust force on a rotating chiral particle, which will push or pull the particle along the rotation axis. The Casimir thrust force comes from two origins: i) the rotation-induced symmetry-breaking in the vacuum and thermal fluctuation and ii) the chiral cross-coupling between electric and magnetic fields and dipoles, which can convert the vacuum spin angular momentum (SAM) to the vacuum force. Using the fluctuation dissipation theorem (FDT), we derive the analytical expressions for the vacuum thrust force in dipolar approximation and the dependences of the force on rotation frequency, temperature and material optical properties are investigated. The work reveals a new mechanism to generate a vacuum force, which opens a new way to exploit zero-point energy of vacuum.

Categories: Journals, Physics