Research Interests:
Research Interests:
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... more
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. This phenomenon is known as the quantum Cheshire cat effect. Here we report the realization of this prediction through joint observation of the spatial and polarization degrees of freedom of a single photon in the two respective arms of an interferometer. Significant pointer shifts ( ~ 50 microns), corresponding to measured weak values, 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 test...
Research Interests:
Research Interests: Physics and Randomness
Research Interests:
Research Interests:
Research Interests:
Efficient certification and quantification of high dimensional entanglement of composite systems are challenging both theoretically as well as experimentally. Here, we demonstrate how to measure the linear entropy, negativity and the... more
Efficient certification and quantification of high dimensional entanglement of composite systems are challenging both theoretically as well as experimentally. Here, we demonstrate how to measure the linear entropy, negativity and the Schmidt number of bipartite systems from the visibility of Mach–Zehnder interferometer using single copies of the quantum state. Our result shows that for any two qubit pure bipartite state, the interference visibility is a direct measure of entanglement. We also propose how to measure the mutual predictability experimentally from the intensity patterns of the interferometric set-up without having to resort to local measurements of mutually unbiased bases. Furthermore, we show that the entanglement witness operator can be measured in a interference setup and the phase shift is sensitive to the separable or entangled nature of the state. Our proposal bring out the power of Interferometric set-up in entanglement detection of pure and several mixed states ...
Research Interests:
Research Interests:
We focus on characterizing entanglement of high dimensional bipartite states using various statistical correlators for two-qudit mixed states. The salient results obtained are as follows: (a) A scheme for determining the entanglement... more
We focus on characterizing entanglement of high dimensional bipartite states using various statistical correlators for two-qudit mixed states. The salient results obtained are as follows: (a) A scheme for determining the entanglement measure given by Negativity is explored by analytically relating it to the widely used statistical correlators viz. mutual predictability, mutual information and Pearson Correlation coefficient for different types of bipartite arbitrary dimensional mixed states. Importantly, this is demonstrated using only a pair of complementary observables pertaining to the mutually unbiased bases. (b) The relations thus derived provide the separability bounds for detecting entanglement obtained for a fixed choice of the complementary observables, while the bounds per se are state-dependent. Such bounds are compared with the earlier suggested separability bounds. (c) We also show how these statistical correlators can enable distinguishing between the separable, distil...
Research Interests:
A hitherto unnoticed feature of quantum steering is demonstrated, namely that, while entanglement is necessary for steering, higher degree of entanglement does not necessarily imply higher degree of quantum steering. This leads to the... more
A hitherto unnoticed feature of quantum steering is demonstrated, namely that, while entanglement is necessary for steering, higher degree of entanglement does not necessarily imply higher degree of quantum steering. This leads to the question as to what aspect of correlation entailed by the quantum state serves as the appropriate quantitative resource for steering. To this end, considering Bell-diagonal states, suitable measures of simultaneous correlations in two and three complementary bases are identified as the relevant quantitative resources for quantum steering involving two- and three-settings respectively. This means that, for steerable Bell-diagonal states, higher value of simultaneous correlations in mutually unbiased bases necessarily implies higher degree of quantum steering.
Research Interests:
Research Interests:
This is a comment on "Strong Measurements Give a Better Direct Measurement of the Quantum Wave Function" which was published as PRL 116, 040502 (2016). We show that there is crucial normalization error in this Letter which... more
This is a comment on "Strong Measurements Give a Better Direct Measurement of the Quantum Wave Function" which was published as PRL 116, 040502 (2016). We show that there is crucial normalization error in this Letter which invalidates the proposal.
Research Interests:
Debarshi Das,1, ∗ Arkaprabha Ghosal,1, † Som Kanjilal,1, ‡ Ananda G. Maity,2, § and Arup Roy3, ¶ Centre for Astroparticle Physics and Space Science (CAPSS), Bose Institute, Block EN, Sector V, Salt Lake, Kolkata 700 091, India S. N. Bose... more
Debarshi Das,1, ∗ Arkaprabha Ghosal,1, † Som Kanjilal,1, ‡ Ananda G. Maity,2, § and Arup Roy3, ¶ Centre for Astroparticle Physics and Space Science (CAPSS), Bose Institute, Block EN, Sector V, Salt Lake, Kolkata 700 091, India S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700 106, India Department of Physics, A B N Seal College, Cooch Behar, West Bengal 736101 India
Research Interests:
Information about an unknown quantum state can be encoded in weak values of projectors belonging to a complete eigenbasis. We present a protocol that enables one party -- Bob -- to remotely determine the weak values corresponding to weak... more
Information about an unknown quantum state can be encoded in weak values of projectors belonging to a complete eigenbasis. We present a protocol that enables one party -- Bob -- to remotely determine the weak values corresponding to weak measurements performed by another spatially separated party -- Alice. The particular set of weak values contains complete information of the quantum state encoded on Alice's ancilla, which enacts the role of the preselected system state in the aforementioned weak measurement. Consequently, Bob can determine the quantum state from these weak values, which can also be termed as remote state determination or remote state tomography. A combination of non-product bipartite resource state shared between the two parties and classical communication between them is necessary to bring this statistical scheme to fruition. Significantly, the information transfer of a pure quantum state of any known dimensions can be effected even with a resource state of lo...