arXiv subjects

C. S. Unnikrishnan

Publications and source records attributed to C. S. Unnikrishnan.

At least 37 records · Page 2Linked to original sources

arXiv2015

Quantum Gravito-Optics: A Light Route from Semiclassical Gravity to Quantum Gravity

Quantum gravity remains an elusive theory, in spite of our thorough understanding of the quantum theory and the general theory of relativity separately, presumably due to the lack of any observational clues. We argue that the theory of quantum gravity has a strong constraining anchor in the sector of gravitational radiation ensuring reliable physical clues, albeit in a limited observable form. In particular, all types of gravitational waves expected to be observable in LIGO-like advanced detectors are fully quantum mechanical states of radiation. Exact equivalence of the full quantum gravity theory with the familiar semiclassical theory is ensured in the radiation sector, in most real situations where the relevant quantum operator functions are normal ordered, by the analogue of the optical equivalence theorem in quantum optics. We show that this is indeed the case for detection of the waves from a massive binary system, a single gravitational atom, that emits coherent radiation. The idea of quantum-gravitational optics can assist in guiding along the fuzzy roads to quantum gravity.

gr-qc↗

arXiv2015

Some remarks on an old problem of radiation and gravity

The assumed universality of the equivalence principle suggests that a particle in a gravitational field has identical physics to one in an accelerated frame. Yet, energy considerations prohibit radiation from a static particle in a gravitational field while the accelerating counterpart emits. Solutions to the fundamental problems of radiation from charges in a gravitational field and consequences to the equivalence principle usually contrast the far-field and global nature of radiation with the local validity of the equivalence principle. Here, we suggest reliable physical solutions that recognizes the essential need for motional currents and the magnetic component for radiation to occur. Our discussion reiterates the need for a fresh careful look at universality of free fall for charged particles in a gravitational field.

gr-qc↗

arXiv2013

Quantum interference-enhanced deep sub-Doppler cooling of 39 K atoms in gray molasses

We report enhanced sub-Doppler cooling of the bosonic atoms of $^{39}$K facilitated by formation of dark states tuned for the Raman resonance in the $Λ-$configuration near the D1 transition. Temperature of about 12 $μ$K is achieved in the two stage D2-D1 molasses and spans a very large parameter region where quantum interference persists robustly. We also present results on enhanced radiation heating with sub-natural linewidth (0.07$Γ$) and signature Fano like profile of a coherently driven 3-level atomic system. The Optical Bloch Equations relevant for the three-level atom in bichromatic light field is solved with the method of continued fractions to show that cooling occurs only for a small velocity class of atoms, emphasizing the need for pre-cooling in D2 molasses stage.

physics.atom-ph↗

arXiv2013

Accelerated Thermalisation of 39K atoms in a Magnetic Trap with Superimposed Optical Potential

We report the rapid accelerated thermalisation of Potassium 39 K atoms loaded in a magnetic trap, in the presence of a single dipole trap beam. More than an order of magnitude reduction in the thermalisation time, to less than a second, is observed with the focused off- resonant beam occupying only 0.01% of the volume of the magnetic trap. The cold atoms are loaded from a Magneto-Optical Trap(MOT) of 39 K that has gone through a compressed MOT and sub-Doppler cooling stage. The atoms are prepared in the magnetically stretched |F = 2, mF = 2> state prior to loading into the hybrid trap. We also report a direct loading of 39 K atoms, prepared in the state |F = 1>, into a single beam dipole trap.

physics.atom-ph↗

arXiv2012

Does Lorentz Force Law Contradict the Principle and Theories of Relativity for Uniform Linear Motion?

I show that no force or torque is generated in cases involving a charge and a magnet with their relative velocity zero, in any inertial frame of reference. A recent suspicion of an anomalous torque and conflict with relativity in this case is rested. What is distilled as `Lorentz force' in standard electrodynamics, with relative velocity as the parameter, is an under-representation of two distinct physical phenomena, an effect due to Lorentz contraction and another due to the Ampere current-current interaction, rolled into one due to prejudice from special relativity applied only to linear motion. When both are included in the analysis of the problem there is no anomalous force or torque, ensuring the validity of Poincare's principle of relativity. The issue of validity of electrodynamics without the concept of absolute rest, however, is subtle and empirically open when general noninertial motion is considered, as I will discuss in another paper.

physics.class-ph↗

arXiv2011

Thermal expansion of the earth and the speed of neutrinos

It is pointed out that one of the systematic effects that can affect the measurement of the speed of neutrinos significantly is the variability of the unaveraged measurement of the distance between two points on the earth due to thermal expansion. Possible difference between estimates done with surface GPS apparatus and the true underground baseline can change substantially the statistical significance of the result of superluminal speed of neutrinos, reported recently.

physics.gen-ph↗

arXiv2011

Rigorous Comparison of Gravimetry Employing Atom Interferometers and the Measurement of Gravitational Time Dilation

We present a gravitationally rigorous and clear answer, in the negative, to the question whether gravimetry with atom interferometers is equivalent to the the measurement of the relative gravitational time dilation of two clocks separated in space. Though matter and light waves, quantum states and oscillator clocks are quantum synonymous through the Planck-Einstein-de Broglie relations and the equivalence principle, there are crucial differences in the context of tests of gravitation theories.

quant-ph↗

arXiv2011

Universality in the Gravitational Stretching of Clocks, Waves and Quantum States

There are discernible and fundamental differences between clocks, waves and physical states in classical physics. These fundamental concepts find a common expression in the context of quantum physics in gravitational fields; matter and light waves, quantum states and oscillator clocks become quantum synonymous through the Planck-Einstein-de Broglie relations and the equivalence principle. With this insight, gravitational effects on quantum systems can be simply and accurately analyzed. Apart from providing a transparent framework for conceptual and quantitative thinking on matter waves and quantum states in a gravitational field, we address and resolve with clarity the recent controversial discussions on the important issue of the relation and the crucial difference between gravimetery using atom interferometers and the measurement of gravitational time dilation.

quant-ph↗

arXiv2011

End of Several Quantum Mysteries

I report on the discovery of quantum compatible local variables that are shared between subsystems of quantum-conventionally entangled physical systems such that they determine the correlations of spatially separated systems while preserving strict Einstein locality. This puts an end to the mystery of spooky action at a distance and alleged collapse at a distance, answering vital questions, first raised in the EPR paper, on the behaviour of spatially separated entangled systems. The solution helps to understand quantitative measures of entanglement in a transparent way. It also provides new insight, consistent with strict locality, of the physics of quantum teleportation and related phenomena.

quant-ph↗

arXiv2010

Precision studies of Casimir force and short-range gravity employing prototypes of interferometric gravitational wave detectors

We discuss experimental schemes to measure the Casimir force and short range forces from hypothetical modified gravity with unprecedented sensitivity using highly sensitive prototype gravitational wave detectors as displacement sensors. The finite temperature effects of the Casimir force would be detectable with a sensitivity of better than 1% for separation exceeding 30 microns. Constraints on short range modifications to gravity can be improved in the distance range of 10-100 microns.

gr-qc↗

arXiv2010

Standard and derived Planck quantities: selected analysis and derivations

We provide an overview of the fundamental units of physical quantities determined naturally by the values of fundamental constants of nature. We discuss a comparison between the 'Planck units', now widely used in theoretical physics and the pre-quantum 'Stoney units' in which, instead of the Planck constant, the charge of the electron is used with very similar quantitative results. We discuss some of the physical motivation for these special units, attributed much after they were introduced, and also put forth a summary of the arguments supporting various cases for making specific physical interpretations of the meanings of some of these units. The new aspects we discuss are a possible physical basis for the Stoney units, their link to the Planck units, and also the importance of Planck units for thermodynamical quantities in the context of quantum gravity.

gr-qc↗

arXiv2008

Proposal for an experiment to search for Randall-Sundrum type corrections to Newton's law of gravitation

String theory, as well as the string inspired brane-world models such as the Randall-Sundrum (RS) one, suggest a modification of Newton's law of gravitation at small distance scales. Search for modifications of standard gravity is an active field of research in this context. It is well known that short range corrections to gravity would violate the Newton-Birkhoff theorem. Based on calculations of RS type non-Newtonian forces for finite size spherical bodies, we propose a torsion balance based experiment to search for the effects of violation of this celebrated theorem valid in Newtonian gravity as well as the general theory of relativity. We explain the main principle behind the experiment and provide detailed calculations suggesting optimum values of the parameters of the experiment. The projected sensitivity is sufficient to probe the Randall-Sundrum parameter up to 10 microns.

hep-th↗

arXiv2004

On the Claim of the Observation of 'Macro-quantum effects' of Magnetic Vector Potential in the Classical Domain

I present conclusive arguments to show that a recent claim of observation of quantum-like effects of the magnetic vector potential in the classical macrodomain is spurious. The `one dimensional interference patterns' referred to in the paper by R. K. Varma et al (Phys. Lett. A 303 (2002) 114-120) are not due to any quantum-like wave phenomena. The data reported in the paper are not consistent with the interpretation of interference, or with the topology of the Aharonov-Bohm effect. The assertion that they are evidence of A-B like effect in the classical macrodomain is based on inadequate appreciation of basic physical facts regarding classical motion of electrons in magnetic fields, interference phenomena, and the A-B effect.

quant-ph↗

arXiv2004

Correlation functions, Bell's inequalities and the fundamental conservation laws

I derive the correlation function for a general theory of two-valued spin variables that satisfy the fundamental conservation law of angular momentum. The unique theory-independent correlation function is identical to the quantum mechanical correlation function. I prove that any theory of correlations of such discrete variables satisfying the fundamental conservation law of angular momentum violates the Bell's inequalities. Taken together with the Bell's theorem, this result has far reaching implications. No theory satisfying Einstein locality, reality in the EPR-Bell sense, and the validity of the conservation law can be constructed. Therefore, all local hidden variable theories are incompatible with fundamental symmetries and conservation laws. Bell's inequalities can be obeyed only by violating a conservation law. The implications for experiments on Bell's inequalities are obvious. The result provides new insight regarding entanglement, and its measures.

quant-ph↗

arXiv2004

Casimir Energy Density at Planck Time: Cosmic Coincidence or Double Solution to the Cosmological Dark Energy Problem?

The Casimir energy density calculated for a spherical shell of radius equal to the size of the Universe projected back to the Planck time is almost equal to the present day critical density. Is it just a coincidence, or is it a solution to the `cosmic dark energy' and the `cosmic coincidence' problems? The correspondence is too close to be ignored as a coincidence, especially since this solution fits the conceptual and numerical ideas about the dark energy, and also answers why this energy is starting to dominate at the present era in the evolution of the Universe.

gr-qc↗

arXiv2004

Spin-Statistics connection and the gravity of the Universe: The Cosmic connection

I suggest that the Spin-Statistics connection is a consequence of the phase shifts on quantum scattering amplitudes due to the induced gravitomagnetic field of the whole Universe at critical density. This connection was recently brought out in the context of a new theory of relativity in flat space with matter, called Cosmic Relativity (gr-qc/0406023). This prediction of the correct gravitational phases is a consequence of any relativistic gravitation theory in the presence of the massive Universe. This can also be interpreted as related to the Mach's principle applied to quantum phenomena. Perhaps this is the simplest valid proof of the Spin-Statistics Theorem, and it finally identifies the physical origin of the connection.

gr-qc↗

arXiv2004

Cosmic Relativity: The Fundamental Theory of Relativity, its Implications, and Experimental Tests

In this paper I argue for a reassessment of special relativity. The fundamental theory of relativity applicable in this Universe has to be consistent with the existence of the massive Universe, and with the effects of its gravitational interaction on local physics. A reanalysis of the situation suggests that all relativistic effects that are presently attributed to kinematics of relative motion in flat space-time are in fact gravitational effects of the nearly homogeneous and isotropic Universe. The correct theory of relativity is the one with a preferred cosmic rest frame. Yet, the theory preserves Lorentz invariance. I outline the new theory of Cosmic Relativity, and its implications to local physics, especially to physics of clocks and to quantum physics. This theory is generally applicable to inertial and noninertial motion. Most significanlty, experimental evidence support and favour Cosmic Relativity. There are observed effects that can be consistently explained only within Cosmic Relativity. The most amazing of these is the dependence of the time dilation of clocks on their `absolute' velocity relative to the cosmic rest frame. Important effects on quantum systems include the physical cause of the Thomas precession responsible for part of the spectral fine structure, and the phase changes responsible for the spin-statistics connection. At a deeper level it is conlcuded that relativity in flat space-time with matter reiterates Mach's principle. There will not be any relativistic effect in an empty Universe.

gr-qc↗

arXiv2002

Nano-constraints on the spatial anisotropy of the Gravitational Constant

We present constraints from various experimental data that limit any spatial anisotropy of the Gravitational constant to less than a part per billion or even smaller. This rules out with a wide margin the recently reported claim of a spatial anisotropy of G with a diurnal temporal signature.

gr-qc↗