Dipankar Home

Dipankar Home
Born	11 November 1955
Citizenship	India
Awards	Homi Bhabha Fellowship Jawaharlal Nehru Fellowship B. M. Birla Science Prize Darshan Vigyan Samman INSA Medal for Young Scientists
Scientific career
Fields	Physics
Institutions	Bose Institute

Dipankar Home is the earliest Indian researcher who did his doctoral work on Foundations of Quantum Mechanics in the beginning of 1980s and has been steadily contributing to this area over the last five decades resulting in 144 peer-reviewed publications and two Research-level Books: “Conceptual Foundations of Quantum Physics – An Overview from Modern Perspectives” (Plenum, 1997), with a Foreword by Nobel laureate Anthony Leggett, and (ii) “Einstein’s Struggles with Quantum Theory: A Reappraisal” (Springer, 2007), co-authored with Andrew Whitaker, having a Foreword by Nobel laureate Roger Penrose. During this period, this line of research has remarkably evolved, leading to fundamentally important experiments, and has provided the basis for a frontier area of science, viz. Quantum Information Theory, alongside its applications in Quantum Communication and Quantum Computation. In fact, this research area has been acclaimed by the Nobel Committee as a “vibrant and rapidly developing field” ushering in the "Second Quantum Revolution" while announcing the Nobel Prizes in Physics 2022 awarded for pioneering works in this area.

Central Themes of the Most Significant Recent Research Works of Home with his collaborators

(A) Investigations on the interplay between foundational issues of Quantum Mechanics and their experimental realizations, exploring novel features of Quantum Mechanics.

(B) Studies on fundamental topics concerning interplay between Quantum Foundations and Quantum Information Theory entailing applications in information transfer/processing protocols.

Highlights

Three of the proposed experiments by Home and his collaborators have been implemented, three other proposed ideas are being pursued for experimental studies. Moreover, Home has contributed to a Theory-Experiment collaboration work which has been experimentally realized, and another such work is under way.

(I) Blending of two fundamental Quantum Features, Indistinguishability and Entanglement

(a) An earlier unnoticed remarkable property of Entanglement arising from Indistinguishability of any two identical particles was uncovered by us, calling it ‘Duality in Entanglement’ [Physical Review Letters 110, 140404 (2013)].

Using photons, our predicted ‘Duality in Entanglement’ was experimentally verified at Tsinghua University, Beijing [New Journal of Physics 16, 083011 (2014)], followed by another photonic experimental study of this property at INRIM, Torino [Physical Review A91, 062117 (2015)]. An interesting application of this property was also pointed out by others for performing entanglement sorting of photons [Physical Review A 91, 062303 (2015)].

(b) A novel scheme towards harnessing Quantum Indistinguishability for an arbitrarily efficient entanglement generation was formulated by us for any two identical Bosons/Fermions originating from two independent sources [Physical Review Letters88, 050401 (2002)].

Such a scheme is of considerable significance since Entanglement lies at the core of Quantum Technology of the 21st Century. While the ideas conceived in this work have been used by others, for example, in the studies concerning Free-electron Quantum Computation [Physical Review Letters 93, 020501 (2004)], the prospect of its experimental realization has now brightened owing to recent notable technological developments concerning molecular two-particle interferometry and non-absorptive path detectors, the two key ingredients of our scheme.

(II) Formulation of a novel testable scheme for evidencing Quantumness and violation of Macrorealism for large mass oscillating objects

Using the currently available state-of-the-art technology, our work [Physical Review Letters 120, 210402 (2018)] has delineated a feasible way of testing Quantumness and violation of Macrorealism for optically trapped and harmonically oscillating nano-objects having mass around 106 – 109 amu, much greater than that possible by other methods realised so far. This would therefore contribute significantly to the contemporary frontier research enterprise of testing the limits of validity of quantum mechanics in the macroscopic domain, which is currently attracting intense explorations. The implementation of our proposal is being pursued by H. Ulbricht and his group at University of Southampton UK.

(III) Introducing the notion of ‘Single Particle (Intraparticle) Entanglement’ and formulating Bell-type inequality for testing Quantum Contextuality

Our work was the earliest to invoke the notion of entanglement between two different dynamical variables of a single particle to formulate Bell-type inequality pertaining to such entanglement [Physics Letters A 102, 159 (1984)] based on the notion of noncontextuality.

We later developed this work by devising an empirically realizable scheme involving path-spin entanglement for a single particle towards experimentally demonstrating Quantum Contextuality for the first time [Physics Letters A 279, 281 (2001)]. This proposed experiment was subsequently performed by the neutron Interferometric group at Atominstitut, Vienna [nature 425, 45 (2003)]. This was followed by theoretical and experimental studies by various groups concerning such single particle entanglement and its applications in quantum information transfer protocols, including our further contributions in this area [Reviewed by S. Azzini et al. in Advanced Quantum Technology, Vol. 3, No. 10 (2020)].

(IV) DNA Molecular scheme for probing the “Schrödinger-Cat” or the Quantum Measurement Problem

DNA molecular analogue of the much-discussed Schrödinger’s Cat example was formulated by us for the first time in the context of the Quantum Measurement Problem in the mesoscopic domain, using the biochemical propertyof photolyase enzyme attachment to uv-absorbed DNA molecules acting as detectors of uv photons[Physical Review Letters 76, 2836 (1996)]. The way this example can provide constraints on the models proposed for addressing this central riddle of Quantum Mechanics was analysed thereby opening up an earlier uncharted area of study.

The futuristic significance of this intriguing work was commented upon in “Encyclopaedia Britannica Book of the Year 1996” (edited by G. M. Edwards), pp. 242-243, as well as in the Review article by A. J. Leggett, J. Phys. Condens. Matter 14, R415 (2002). In view of the recent advances in studies towards using biomolecular systems for investigating fundamental quantum issues, further development of our original proposal by making it more empirically relevant for probing the much debated aspects of the Quantum Measurement Problem is gaining more topical significance.

(V) Revealing an earlier unexplored facet of wave-particle duality of single photons

A testable experiment was proposed by us predicting wave-like optical tunneling as well as particle-like anticoincidences of single photons in the same setup for a double-prism device [Physics Letters A 153, 403 (1991); 168, 95 (1992)], implemented at the Hamamatsu Photonics Central Research Laboratory, Japan [Physics Letters A 168, 1 (1992)] demonstrating a novel aspect of wave-particle duality. This provided a stimulating twist to the Bohrian principle of Wave-Particle Complementarity by going beyond its usual domain of application concerning single particle interference vis-à-vis which-path determination. Conceptual implications of this work had evoked considerable discussions in a number of books. Further, the double-prism device for single photonic experiment developed for this purpose at the Hamamatsu Laboratory had interesting applications.

(VI) Theory-Experiment Collaboration Work: Single photon based interferometric loophole-free test of the temporal analogue of Bell inequality, viz. the Leggett-Garg inequality

This work developed with the required theoretical inputs, in collaboration with U. Sinha’s experimental quantum optics group at Raman Research Institute, Bangalore, resulted in an unambiguous demonstration of the empirical violation of Leggett-Garg inequality, thereby decisively repudiating the notion of realism for single photons, by closing all the relevant loopholes (including the most important ones, detection efficiency and clumsiness loopholes) using appropriately devised strategies for the first time [Physical Review X Quantum 3, 010307 (2022)].

Thus, this experimental platform provides a powerful means for certifying inherent nonclassicality of single photons which can be reliably and efficiently harnessed towards Quantum Communication based applications for which the single photon is a ubiquitous workhorse.

(VII) Exploring novel uses of the Leggett-Garg inequality having fundamental implications

(a) Persistence of quantum mechanical violation of the Leggett-Garg inequality implying incompatibility with the notion of macrorealism was demonstrated for the first time for arbitrarily large spins even under the coarsening of measurement times, coupled with the coarsening of measurement outcomes [Physical Review A 94, 052110 (2016) Physical Review A 100, 042114 (2019)]. The striking feature, thus, revealed entailing that classicality for large spin does not emerge from quantum mechanics, whatever be the form and degree of ‘unsharpness’ or course graining of the measurements, has deep-seated implications concerning the much investigated and debated issue of the classical limit of quantum mechanics.

(b) Our work [Physical Review A 88, 022115 (2013)] was the first to probe quantum mechanical violation of the temporal analogue of Bell inequality, viz. the Leggett-Garg inequality in the context of weak interaction induced two state oscillations of neutral kaons and neutrinos. A remarkable result was obtained that this violation for the kaon oscillation is enhanced due to CP noninvariance, while, for the neutrino oscillation, such violation is sensitively dependent on the value of the mixing parameter. This work opened up a potentially rich area, followed by a number of studies, including an important experiment [Physical Review Letters 117, 050402 (2016)] demonstrating quantum mechanically predicted violation of the Leggett-Garg inequality for neutrino oscillation over a length scale of nearly 700 km. Further studies are under way, including probing deeper the implications of this experiment, along with that of the findings of our initiating work on this topic.

(VIII) Generalising Wigner’s approach for detecting multipartite nonlocality

Distinct from Bell’s approach, Wigner had suggested an elegant formulation of local realist inequality for showing quantum nonlocality. However, Wigner’s original scheme was restricted to only bipartite maximally entangled states, and hence was largely ignored. Our work [Physical Review A 91, 012102 (2015)] was the first to successfully generalise Wigner’s approach towards detecting nonlocality of an arbitrary multipartite entangled state by deriving appropriate local realist multipartite inequalities. Thus, this paper opened up an earlier unexplored direction for studying multipartite nonlocality, a topic which is of much contemporary interest.

Very recently, we followed up our earlier above mentioned work by showing that Wigner’s approach can be further developed by deriving a suitable set of local realist multipartite inequalities whose quantum mechanical violation would not only rigorously certify multipartite nonlocality for any multipartite entangled state, but would also enable detecting whether there is any particular bipartition of the multipartite system which is nonlocally correlated for cases where not all different bipartitions are nonlocally correlated [Physical review A 106, 062203 (2022)]. This additional feature provides our formulated extension of Wigner’s scheme a significant advantage compared to other standard multipartite nonlocality detection scheme based on using the Svatlichny inequality. The efficacy of our scheme has been comprehensively illustrated for the tripartite and quadripartite states.

(IX) Using Pearson Correlators for Certifying and Quantifying High Dimensional Entanglement

In view of considerable advantages provided by the high dimensional entangled states for ensuring efficient and robust applications in Quantum Communication, the certification and quantification of high dimensional entanglement is of much topical importance. In this context, our work [Physical Review A 101, 022112 (2020)] has initiated a novel direction of study in terms of the empirically measurable statistical correlator known as the Pearson Correlator, which we have analytically related with a suitable entanglement measure like Negativity for a range of bipartite qutrit states using only a pair of complementary observables. This approach, therefore, opens up unique empirical means for exactly quantifying such high dimensional entanglement. Extension of this scheme for a wider class of high dimensional bipartite entangled states using Pearson Correlator and other statistical correlators like Mutual Predictability and Mutual Information is a promising area of research with multifold applications in Quantum Information and Quantum Communication, and our research work along this direction is currently in progress.

(X) Appropriate Quantification of the effectiveness of any resource state for implementing Remote State Preparation

In this work [Physical Review A 98, 062320 (2018)] we show that an appropriate measure of simultaneous correlations in mutually unbiased bases can serve as a powerful quantifier of the usefulnessof a resource state for Remote State Preparation (RSP) based on entangled as well as separable states, even using zero-discord states. Given the importance of RSP as a key Quantum Information Processing task, further works harnessing the potentiality of our novel approach should be of considerable significance.

(XI) Identifying the appropriate quantitative resource for Quantum Steering

Besides its profound fundamental implications, the phenomenon of Quantum Steering has wide-ranging useful Quantum Information Processing applications. However, an outstanding issue underlying such applications is the question concerning what aspect of Quantum Correlation can serve as the appropriate quantitative resource for Quantum Steering. This has, surprisingly, remained unaddressed. It is in this work [Physical Review A 98, 042306 (2018)] we have resolved this issue by analytically relating an appropriate measure of simultaneous correlations in mutually unbiased bases to the standard measure of Quantum Steering used for two-qubit states so that a higher value of the measure of such correlations implies a higher degree of Quantum Steering. This scheme, thus, opens up promising line of studies towards further developing this approach and exploring its potential applications by harnessing Quantum Steering in areas like Quantum Communication.

Currently Co-investigator of the following Research Programmes with various collaborators

(A) A Theory-Experiment collaboration work is nearing completion which seeks to realize for the first time joint detection of spatial and polarization degrees of freedom of a single photon in the two respective arms of an interferometer in each run. This is being achieved by implementing in each arm of the interferometer, non-destructive, minimally-disturbing interaction which couples a suitable particle property to a pointer while maintaining the path superposition. Such an experiment would constitute an unambiguous demonstration of what has been called the Quantum Cheshire Cat effect entailing spatial separation between different properties of an individual particle within an interferometer. This intriguing effect has far-reaching conceptual implications and potentiality for interesting applications in the context of information transfer/processing protocols.

(B) In the context of the topically important challenging enterprise of testing the limits of applicability of quantum mechanics, a novel scheme is being formulated capable of demonstrating mass-independent quantumness of a massive object which is realisable with the state-of-the-art technology having potential rich applications, while our proposed scheme offers the tantalizing prospect of scaling up the test of quantumness, all the way to arbitrarily massive linear oscillators.

(C) Using the novel idea of massive spatial qubits, we are formulating a testable proposal for evidencing macro-nonclassicality as well as Casimir interaction induced entanglement between two neutral nano-objects of mass about billion – trillion times more than hydrogen atom. This would enable testing for the first time quantumness of Casimir interaction persisting in the macroscopic domain.

(D) Developing further our earlier work initiating the method for determining bipartite higher dimensional entanglement measures using observable statistical correlators, a comprehensive study is in progress for analytically relating an entanglement measure like Negativity with the statistical correlators like Pearson Correlator, Mutual Predictability, and Mutual Information for a range of empirically relevant bipartite arbitrary dimensional mixed entangled states, importantly using only a pair of complementary observables. This study is, therefore, of much significance towards exactly quantifying arbitrary dimensional bipartite entangled states, thereby enabling their effective use in various applications involving information transfer/processing protocols. Extension of this study for tripartite arbitrary dimensional entangled states is also in progress.

(E) A comprehensive research programme is being pursued for certifying and quantifying Genuine Random Numbers based on harnessing Quantum Nonlocality through the use of Hardy and Cabello-Liang type nonlocality arguments, involving also the study of quantitative relationship between nonlocality and randomness. Such a study is of much topical importance in view of the crucial role played by Genuine Random Numbers for ensuring secure encryption of information in Quantum Communication, even while using untrustworthy devices.

(F) Investigations are being pursued for devising novel uses of entanglement between different dynamical variables of a single particle (called “intraparticle” or “single particle entanglement”) in the context of various information transfer/processing protocols, including Quantum Cryptography.

(G) Fresh perspective is being explored on the nature of Quantum Nonlocality by invoking Local Friendliness inequality andusing a modified Einstein-Podosky-Rosen-Bohm setup. Further, the nonlocal feature of Quantum Teleportation is being probed using preparation contextuality inequality for the first time in this context, seeking to provide fresh insight into the way nonlocality occurs in Quantum Teleportation.

(H) Investigating critically the basis of Larmor procession and seeking to reveal how spatial-spin coupling in a single spin ½ particle wavefunction can induce deviation from Larmor precession which persists for significantly large masses and can have applications for quantum sensing.