Bose Institute

A Brief Summary of the Significant Scientific Contributions

Dipankar Home is one of the early Indian researchers to have initiated investigations on Foundational issues of Quantum Mechanics since 1980s and was the first Indian researcher to have done his Ph. D. work on this topic. This line of study has gradually evolved to become amenable to a variety of fundamentally important experiments, as well as has become intimately related to the currently one of the frontier areas of science, viz. Quantum Information Theory and its applications in Quantum Communication, Quantum Cryptography and Quantum Computation.

Among his 137 Research Publications with his various collaborators that have been cited in 20 Books, and that have Total Citation Number around 1967 (Google Scholar), Home’s notable contribution has been Two distinctive 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 Roger Penrose. Both these books have been peer-appreciated in Physics Today (October, 1998 and May, 2008 respectively), apart from the former being also appreciatively reviewed in The Times (London), Higher Education Supplement (25 September, 1998), Foundations of Physics, Vol. 31, pp. 855 -857 (2001), and in Progress in Quantum Electronics, Vol. 22, pp. 41-42 (1998) by some of the leading experts in the area of Quantum Foundations. These two books have Total Citation Number around 229 (Google Scholar).

Among the manifold research works of Home with his collaborators, the most significant ones are briefly mentioned as follows:

A) At the core of the various intriguing questions raised by Einstein, Schrödinger and others about foundational aspects of Quantum Mechanics (QM) is the QM incompatibility with the everyday notion of Macrorealism (MR) which assumes that, at any instant, a system is in a definite state having definite properties, irrespective of any measurement. The latest work by Home and his collaborators [Physical Review Letters 120, 210402 (2018)] opens up a novel direction for extending the tests of MR as well as of the nonclassicality of QM for massive systems much beyond those possible by other methods.

In particular, using the Leggett-Garg inequality, the work by Home and his collaborators shows that the QM violation of MR for large mass systems is testable for a system like harmonic oscillator which has a well defined classical description and is initially in a state which is the most classical-like of all quantum states, viz. the harmonic oscillator coherent state. Testing of this scheme using the setup proposed in this work for optically trapped and oscillating nano-scale objects of mass about million to billion times heavier than hydrogen atoms is being implemented by Hendrik Ulbricht and his group at University of Southampton, UK.

B) A hitherto unexplored connection was revealed between two profound features of QM, viz. Quantum Indistinguishability (QI) and Quantum Entanglement (QE) by invoking QI for formulating an arbitrarily efficient generic scheme that can entangle, using any spin-like variable, any two identical bosons/fermions coming from independent sources [Physical Review Letters 88, 050401 (2002)].

Such an efficient generic scheme for generating QE is of considerable importance since QE lies at the core of Quantum Foundations and various applications of Quantum Information Theory. Furthermore, this work suggested a novel form of complementarity between particle distinguishability and the amount of entanglement generated, besides providing one of the ingredients of the seminal work by C. W. J. Beenakker et al. [Physical Review Letters 93, 020501 (2004)] which initiated studies on Free-Electron Quantum Computation.

C) The above-mentioned line of study blending QI and QE was enriched by uncovering an earlier unnoticed property of QE involving any two identical particles which has been called ‘Duality in Entanglement’ [Physical Review Letters 110, 140404 (2013)]. Importantly, this property enables studying the transition from QI to Classical Distinguishability, as well as can be an effective tool for empirically probing aspects of QI for mesoscopic/macroscopic molecules without requiring to bring them together, thereby avoiding the effect of interaction between them.

For photons, this predicted property of ‘Entanglement Duality’ (involving the manifestation of polarization entanglement when the photons are labelled by different momenta, or, for the same source, manifesting momentum entanglement when the photons are labelled by polarization variables) has been experimentally verified at Tsinghua University, Beijing [New Journal of Physics 16, 083011 (2014)], followed by another experimental study at INRIM, Torino [Physical Review A 91, 062117 (2015)] using Bell measurements in order to probe a few subtle aspects of our predicted ‘Entanglement Duality’.

D) One of the earliest ideas for testing the fundamental property of Quantum Contextuality was formulated by introducing the notion of path-spin intraparticle entanglement as applied to a Bell-type inequality involving the path and spin variables pertaining to a single spin-1/2 particle [Physics Letters A 279, 281 (2001)].

This was experimentally verified by the Neutron Interferometric group at Atominstitut, Vienna [Nature 425, 45 (2003)].

E) A novel manifestation of wave-particle duality of single photon states providing fresh insights into the Bohrian principle of wave particle complementarity was formulated by invoking the quantum mechanical treatment of tunneling of single photon states in the context of a double-prism device [Physics Letters A 153, 403 (1991); 168, 95 (1992)].

This proposal was experimentally realized at the Hamamatsu Photonics Central Research Laboratory, Japan [Physics Letters A 68, 1 (1992)].

F) A striking biomolecular example was formulated in order to empirically probe aspects of the Quantum Measurement Problem in the mesoscopic domain [Physical Review Letters 76, 2836 (1996)] by using the biochemical property of photolyase enzyme attachment to uv-absorbed DNA molecules serving as detectors of uv photons. This work was one of the earliest of its kind, using the biomolecular phenomenon in order to provide empirically relevant constraints on the various approaches seeking to address the much debated Quantum Measurement Problem.

G) A series of investigations concerning an intriguing Quantum Mechanical effect known as the Quantum Zeno Effect (inhibition of the time evolution of a system due to repeated projective measurements) throwing light on the various critical aspects of its treatment, its deep-seated conceptual implications and clarifying the question of its experimental realizability, culminated in a comprehensive and widely cited in-depth analysis [Annals of Physics 258, 237 (1997)] of this effect which is now well recognized as one of the key fundamental quantum features.

H) Wigner’s argument seeking to demonstrate Quantum Nonlocality that was originally formulated only for bipartite states has been successfully generalized for an arbitrary multipartite state, thereby providing a powerful method for obtaining multipartite Bell-type inequalities in order to probe Quantum Nonlocality pertaining to the states of multipartite systems [Physical Review A 91, 012102 (2015)]. The efficacy of such obtained multipartite Bell-type inequalities has been demonstrated for the quadripartite entangled states, thus opening up a novel direction in this area of study concerning multipartite Quantum Nonlocality which is of much contemporary interest.

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