Ph.D, MSc

Dr. T. Subeesh obtained his Masters degree in Physics from Indian Institute of Technology Madras, Chennai. He received his PhD from Indian Institute of Technology Madras, Chennai for his work on Phase Properties of Radiation Fields. His areas of research include Theoretical Quantum Optics and Biomedical Instrumentation. He has also qualified National Eligibility Test (NET) for Lectureship, conducted by University Grants Commission (UGC), Government of India.


Publication Type: Journal Article

Year of Publication Title


Dr. Subeesh T. and Sudhir, Vc, “Phase properties of operator valued measures in phase space”, Journal of Modern Optics, vol. 60, pp. 503-508, 2013.[Abstract]

<p>The Wigner phase operator (WPO) is identified as an operator valued measure (OVM) and its eigenstates are obtained. An operator satisfying the canonical commutation relation with the Wigner phase operator is also constructed and this establishes a Wigner distribution based operator formalism for the Wigner phase distribution. It is then argued that the WPO cannot represent a projective measurement of the phase; but is in fact to be interpreted as an operator valued measure for the phase. The non-positivity of the latter can be overcome by defining a positive operator valued measure (POVM) via a proper filter function, based on the view that phase measurements are coarse-grained in phase space, leading to the well known Q-distribution. The identification of the Q phase operator as a POVM is in good agreement with the earlier observation regarding the relation between operational phase measurement schemes and the Q-distribution. The Q phase POVM can be dilated in the sense of Gelfand-Naimark, to an operational setting of interference at a beam-splitter with another coherent state - this results in a von Neumann projector with well-defined phase in the expanded Hilbert space of the two modes. © 2013 Copyright Taylor and Francis Group, LLC.</p>

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Dr. Subeesh T., Sudhir, Vc, Ahmed, A. B. Mad, and Satyanarayana, MaVenkata, “Effect of squeezing on the atomic and the entanglement dynamics in the jaynes-cummings model”, Nonlinear Optics Quantum Optics, vol. 44, pp. 245-258, 2012.[Abstract]

<p>The dynamics of the Jaynes-Cummings interaction of a two-level atom interacting with a single mode of the radiation field is investigated, as the state of the field is gradually changed from a coherent state to a squeezed coherent state. The effect of mild squeezing on the coherent light is shown to be striking: the photon number distribution gets localized and it peaks maximally for a particular value of squeezing. The atomic inversion retains its structure for a longer time. The mean linear entropy shows that the atom has a tendency to get disentangled from field within the collapse region and also in the revival region, for mild squeezing. These properties are absent for the case of a coherent state or for an excessively squeezed coherent state. We also elucidate a connection between these properties and the photon statistics of the mildly squeezed coherent state; these states have the minimum variance and are also maximally sub-Poissonian. © 2012 Old City Publishing, Inc.</p>

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Dr. Subeesh T. and Sudhir, V., “Operator formalism for the Wigner phase distribution”, Journal of Modern Optics, vol. 58, pp. 761–765, 2011.[Abstract]

We construct a Hermitian phase operator for the radially integrated Wigner distribution, which is known to be sensitive to phase. We show that this operator is complete and also elucidate a set of complete but non-orthogonal states that seems to be naturally associated with such an operator. Further, we show that our operator satisfies a weak equivalence relation with the Pegg–Barnett operator, thus showing that the essential phase information furnished by both formalisms are the same. It is also shown that this operator gives results which are in agreement with the expected uniform phase distribution of a Fock state.

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