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Surya Narayan Sahoo

Publications and source records attributed to Surya Narayan Sahoo.

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Collective Behavior of Intelligent Active Brownian Particles in the Presence of a Static Obstacle

Using computer simulations, we investigate the collective behavior of two-dimensional active Brownian particles (ABPs) with excluded-volume interactions in the bulk and in the presence of a single static circular obstacle. Perception-mediated interactions are introduced through a vision-based steering mechanism that enables each particle to reorient its propulsion direction according to the instantaneous positions of neighboring particles within a prescribed vision cone. In the bulk, these intelligent active Brownian particles (iABPs) exhibit distinct collective states, including aggregated clusters, worm-like chains, worm-aggregate coexistence, and dilute gas phases. We characterize these states using a shape anisotropy parameter and construct the corresponding phase diagrams. The presence of a static obstacle, which interacts with the particles through purely repulsive forces, qualitatively alters their collective behavior. In contrast to conventional ABPs, whose isotropic accumulation around the obstacle increases with activity, iABPs exhibit the opposite trend, with boundary accumulation decreasing as the activity increases. We further identify empirical scaling relations that describe particle accumulation and cluster formation at the obstacle boundary. Consequently, the relative effective diffusion coefficient of iABPs displays a nonmonotonic dependence on self-propulsion speed, whereas that of conventional ABPs decreases monotonically with increasing activity. In addition, we show that the residence times of iABPs are orders of magnitude shorter than those of conventional ABPs, indicating that perception-mediated interactions can be useful for controlling the organization and transport of active particles in complex environments.

cond-mat.soft

Reconfigurable circular polarization medium frequency atomic receiver using magneto-electric effect

Nonlinear magnetoelectric effect(NME) in alkali atomic vapor has applications in precision magnetometry in the radio-frequency domain. We report the application of the NME in alkali atomic vapors for projective measurement of medium-frequency (MF) magnetic fields in a circular basis with an extinction ratio up to 500:1 . Utilizing a longitudinal static magnetic field, we demonstrate a high-sensitivity technique for characterizing the ellipticity of radio-frequency (RF) magnetic fields which can in turn be used for phase sensitive detection in mid frequency communication. Additionally, we demonstrate the conversion of binary phase shift keyed RF magnetic fields into amplitude modulation of generated optical fields, a versatile receiver for communication using the medium frequency band.

physics.atom-ph

Unambiguous joint detection of spatially separated properties of a single photon in the two arms of an interferometer

The quantum superposition principle implies that a particle entering an interferometer evolves by simultaneously taking both arms. If a non-destructive, minimally-disturbing interaction coupling a particle property to a pointer is implemented on each arm while maintaining the path superposition, quantum theory predicts that, for a fixed state measured at the output port, certain particle properties can be associated with only one or the other path. Here we report realization of this prediction through joint observation of the spatial and polarization degrees of freedom of a single photon in the two arms of an interferometer. Significant pointer shifts ($\sim$50 microns) are observed in each arm. This observation, involving coupling distinct properties of a quantum system in spatially separated regions, opens new possibilities for quantum information protocols and for tests of quantumness for mesoscopic systems.

quant-ph

Quantum State Interferography

Quantum State Tomography (QST) has been the traditional method for characterization of an unknown state. Recently, many direct measurement methods have been implemented to reconstruct the state in a resource efficient way. In this letter, we present an interferometric method, in which, any qubit state, whether mixed or pure, can be inferred from the visibility, phase shift and average intensity of an interference pattern using a single shot measurement -- hence, we call it Quantum State Interferography. This provides us with a "black box" approach to quantum state estimation, wherein, between the incidence of the photon and extraction of state information, we are not changing any conditions within the set-up, thus giving us a true single shot estimation of the quantum state. In contrast, standard QST requires at least two measurements for pure state qubit and at least three measurements for mixed state qubit reconstruction. We then go on to show that QSI is more resource efficient than QST for quantification of entanglement in pure bipartite qubits. We experimentally implement our method with high fidelity using the polarisation degree of freedom of light. An extension of the scheme to pure states involving $d-1$ interferograms for $d$-dimensional systems is also presented. Thus, the scaling gain is even more dramatic in the qudit scenario for our method where in contrast, standard QST, without any assumptions, scales roughly as $d^2$.

quant-ph

Comment on "Observing the "quantum Cheshire cat" effect with noninvasive weak measurement''

In a very recent work [arXiv:2004.07451], Kim et al claimed to have made the first genuine experimental observation of the Quantum Cheshire Cat effect. We dispute this claim on the ground that the setup employed is not adequate for making the weak measurements that define this interferometric effect. Half of the necessary weak values are not observed, and the other half is obtained indirectly by combining results measured with distinct setups.

quant-ph

Single photon sources: ubiquitous tools in quantum information processing

Quantum technologies are the next big revolution in information technologies, computing, communication security, sensing as well as metrology. What do you use to explore all these fascinating applications when you work in Optics? Photons of course. In this review, we discuss the different available single photon source technologies, compare and contrast them in terms of applicability and properties, discuss state of the art and conclude that the future is indeed bright!

quant-ph

Measuring average of non-Hermitian operator with weak value in a Mach-Zehnder interferometer

Quantum theory allows direct measurement of the average of a non-Hermitian operator using the weak value of the positive semidefinite part of the non-Hermitian operator. Here, we experimentally demonstrate the measurement of weak value and average of non-Hermitian operators by a novel interferometric technique. Our scheme is unique as we can directly obtain the weak value from the interference visibility and the phase shift in a Mach Zehnder interferometer without using any weak measurement or post selection. Both the experiments discussed here were performed with laser sources, but the results would be the same with average statistics of single photon experiments. Thus, the present experiment opens up the novel possibility of measuring weak value and the average value of non-Hermitian operator without weak interaction and post-selection, which can have several technological applications.

quant-ph

Measuring the deviation from the superposition principle in interference experiments

The Feynman Path Integral formalism has long been used for calculations of probability amplitudes. Over the last few years, it has been extensively used to theoretically demonstrate that the usual application of the superposition principle in slit based interference experiments is often incorrect. This has caveat in both optics and quantum mechanics where it is often naively assumed that the boundary condition represented by slits opened individually is same as them being opened together. The correction term comes from exotic sub leading terms in the Path Integral which can be described by what are popularly called non-classical paths. In this work, we report an experiment where we have a controllable parameter that can be varied in its contribution such that the effect due to these non-classical paths can be increased or diminished at will. Thus, the reality of these non-classical paths is brought forth in a classical experiment using microwaves, thereby proving that the boundary condition effect being investigated transcends the classical-quantum divide. We report the first measurement of a deviation (as big as $6\%$) from the superposition principle in the microwave domain using antennas as sources and detectors of the electromagnetic waves. We also show that our results can have potential applications in astronomy.

quant-ph