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Quantum Geometry and Interferometry  [PDF]
Craig Hogan
Physics , 2012,
Abstract: All existing experimental results are currently interpreted using classical geometry. However, there are theoretical reasons to suspect that at a deeper level, geometry emerges as an approximate macroscopic behavior of a quantum system at the Planck scale. If directions in emergent quantum geometry do not commute, new quantum-geometrical degrees of freedom can produce detectable macroscopic deviations from classicality: spatially coherent, transverse position indeterminacy between any pair of world lines, with a displacement amplitude much larger than the Planck length. Positions of separate bodies are entangled with each other, and undergo quantum-geometrical fluctuations that are not describable as metric fluctuations or gravitational waves. These fluctuations can either be cleanly identified or ruled out using interferometers. A Planck-precision test of the classical coherence of space-time on a laboratory scale is now underway at Fermilab.
Quantum interferometry with three-dimensional geometry  [PDF]
N. Spagnolo,L. Aparo,C. Vitelli,A. Crespi,R. Ramponi,R. Osellame,P. Mataloni,F. Sciarrino
Physics , 2013, DOI: 10.1038/srep00862
Abstract: Quantum interferometry uses quantum resources to improve phase estimation with respect to classical methods. Here we propose and theoretically investigate a new quantum interferometric scheme based on three-dimensional waveguide devices. These can be implemented by femtosecond laser waveguide writing, recently adopted for quantum applications. In particular, multiarm interferometers include "tritter" and "quarter" as basic elements, corresponding to the generalization of a beam splitter to a 3- and 4-port splitter, respectively. By injecting Fock states in the input ports of such interferometers, fringe patterns characterized by nonclassical visibilities are expected. This enables outperforming the quantum Fisher information obtained with classical fields in phase estimation. We also discuss the possibility of achieving the simultaneous estimation of more than one optical phase. This approach is expected to open new perspectives to quantum enhanced sensing and metrology performed in integrated photonic.
Quantum-inspired interferometry with chirped laser pulses  [PDF]
R. Kaltenbaek,J. Lavoie,D. N. Biggerstaff,K. J. Resch
Physics , 2008, DOI: 10.1038/nphys1093
Abstract: We introduce and implement an interferometric technique based on chirped femtosecond laser pulses and nonlinear optics. The interference manifests as a high-visibility (> 85%) phase-insensitive dip in the intensity of an optical beam when the two interferometer arms are equal to within the coherence length of the light. This signature is unique in classical interferometry, but is a direct analogue to Hong-Ou-Mandel quantum interference. Our technique exhibits all the metrological advantages of the quantum interferometer, but with signals at least 10^7 times greater. In particular we demonstrate enhanced resolution, robustness against loss, and automatic dispersion cancellation. Our interferometer offers significant advantages over previous technologies, both quantum and classical, in precision time delay measurements and biomedical imaging.
Measurement of Air Temperature using Laser Interferometry  [PDF]
Ahmad Hadi Ali
Journal of Applied Sciences , 2011,
Abstract: Measurement of gas temperature is very crucial in laser induced plasma (LIP) and laser material interaction (LMI). Temperature monitoring devices such as thermocouple has some limitations. The thermocouple cannot be placed at the laser-focusing region since it will induce unwanted external effect. To overcome, a non-contact method is proposed by using interferometric technique. A simple Michelson interferometric was aligned to detect the pressure and refractive index change of ambient air. The temperature gradient of air were recorded and analyzed by using a video camera and phototransistors. From the observation results, it clearly shown that the change of air temperature in one arm of the interferometer will result in the fringes shift of the interference pattern.
Measurement of Quantum Fluctuations in Geometry  [PDF]
Craig J. Hogan
Physics , 2007, DOI: 10.1103/PhysRevD.77.104031
Abstract: A particular form for the quantum indeterminacy of relative spacetime position of events is derived from the limits of measurement possible with Planck wavelength radiation. The indeterminacy predicts fluctuations from a classically defined geometry in the form of ``holographic noise'' whose spatial character, absolute normalization, and spectrum are predicted with no parameters. The noise has a distinctive transverse spatial shear signature, and a flat power spectral density given by the Planck time. An interferometer signal displays noise due to the uncertainty of relative positions of reflection events. The noise corresponds to an accumulation of phase offset with time that mimics a random walk of those optical elements that change the orientation of a wavefront. It only appears in measurements that compare transverse positions, and does not appear at all in purely radial position measurements. A lower bound on holographic noise follows from a covariant upper bound on gravitational entropy. The predicted holographic noise spectrum is estimated to be comparable to measured noise in the currently operating interferometer GEO600. Because of its transverse character, holographic noise is reduced relative to gravitational wave effects in other interferometer designs, such as LIGO, where beam power is much less in the beamsplitter than in the arms.
Optimal quantum-enhanced interferometry using a laser power source  [PDF]
Matthias D. Lang,Carlton M. Caves
Physics , 2013, DOI: 10.1103/PhysRevLett.111.173601
Abstract: We consider an interferometer powered by laser light (a coherent state) into one input port and ask the following question: what is the best state to inject into the second input port, given a constraint on the mean number of photons this state can carry, in order to optimize the interferometer's phase sensitivity? This question is the practical question for high-sensitivity interferometry. We answer the question by considering the quantum Cram{\'e}r-Rao bound for such a setup. The answer is squeezed vacuum.
Entanglement of macroscopic test masses and the Standard Quantum Limit in laser interferometry  [PDF]
Helge Mueller-Ebhardt,Henning Rehbein,Roman Schnabel,Karsten Danzmann,Yanbei Chen
Physics , 2007, DOI: 10.1103/PhysRevLett.100.013601
Abstract: We show that the generation of entanglement of two heavily macroscopic mirrors with masses of up to several kilograms are feasible with state of the art techniques of high-precision laser interferometry. The basis of such a demonstration would be a Michelson interferometer with suspended mirrors and simultaneous homodyne detections at both interferometer output ports. We present the connection between the generation of entanglement and the Standard Quantum Limit (SQL) for a free mass. The SQL is a well-known reference limit in operating interferometers for gravitational-wave detection and provides a measure of when macroscopic entanglement can be observed in the presence of realistic decoherence processes.
Quantum limits to the measurement of spacetime geometry  [PDF]
Seth Lloyd
Physics , 2005,
Abstract: This letter analyzes the limits that quantum mechanics imposes on the accuracy to which spacetime geometry can be measured. By applying the physics of computation to ensembles of clocks, as in GPS, we present a covariant version of the quantum geometric limit, which states that the total number of ticks of clocks and clicks of detectors that can be contained in a four volume of spacetime of radius r and temporal extent t is less than or equal to rt/pi x_P t_P, where x_P, t_P are the Planck length and time. The quantum geometric bound limits the number of events or `ops' that can take place in a four-volume of spacetime and is consistent with and complementary to the holographic bound which limits the number of bits that can exist within a three-volume of spacetime.
Quantum Interferometry, Measurement and Objectivity: Some Basic Features Revisited  [PDF]
Markus Simonius
Physics , 1997,
Abstract: The reduction paradigm of quantum interferometry and the objectivation problem in quantum measurements are reanalyzed. Both are shown to be amenable to straightforward mathematical treatment within "every-users" simple-minded quantum mechanics without reduction postulate etc., using only its probabilistic content.
Measurement-Only Topological Quantum Computation via Anyonic Interferometry  [PDF]
Parsa Bonderson,Michael Freedman,Chetan Nayak
Physics , 2008, DOI: 10.1016/j.aop.2008.09.009
Abstract: We describe measurement-only topological quantum computation using both projective and interferometrical measurement of topological charge. We demonstrate how anyonic teleportation can be achieved using "forced measurement" protocols for both types of measurement. Using this, it is shown how topological charge measurements can be used to generate the braiding transformations used in topological quantum computation, and hence that the physical transportation of computational anyons is unnecessary. We give a detailed discussion of the anyonics for implementation of topological quantum computation (particularly, using the measurement-only approach) in fractional quantum Hall systems.
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