Date of Submission


Date of Award


Institute Name (Publisher)

Indian Statistical Institute

Document Type

Doctoral Thesis

Degree Name

Doctor of Philosophy

Subject Name



Theoretical Statistics and Mathematics Unit (TSMU-Kolkata)


Goswami, Debashish (TSMU-Kolkata; ISI)

Abstract (Summary of the Work)

Motivated by the major role played by probabilistic models in many areas of science, several quantum (i.e. non-commutative) generalizations of classical probability have been attempted by a number of mathematicians. The pioneering works of K.R. Parthasarathy, L. Accardi, R.L. Hudson, P.A. Meyer and others led to the development of one such non-commutative model called ‘quantum probability’ which has a very rich theory of quantum stochastic calculus a la Hudson and Parthasarathy. Within the framework of quantum stochastic calculus, the ‘grand design’ that engages us is the canonical construction and study of ∗-homomorphic flows (jt)t≥0 on a given C ∗ or von-Neumann algebra of observables, say A, where jt : A → A" ⊗ B(Γ(L 2 (R+, k0))) satisfies a differential equation of the formdjt(·) = jt(θ µ ν (·))Λν µ (dt),Λ ν µ (dt) being the well-known quantum stochastic integrators in the Fock-space Γ(L 2 (R+, k0)) (see for example [52]), with k0 being a Hilbert space called the noise space. The vacuum expectation semigroup of the flow, generated by θ 0 0 (·), is a contractive semigroup of completely positive maps on the said algebra. In the realm of classical probability, such semigroups are typically the expectation semigroups associated with Markov processes. Of particular importance are the so called heat semigroups on Riemannian manifolds, which are the expectation semigroups associated with manifold-valued Brownian motions. The quantum analogue of ‘dilation problem’, i.e. to construct a Markov process from its expectation semigroup, is very interesting and important in quantum probability too.There is an interesting confluence of Riemannian geometry and classical stochastic process, under the framework of ‘stochastic geometry’. In particular there are interesting connections between the geometry of a Riemannian manifold and the probabilistic information obtained from a Brownian motion taking value in the manifold. For example, the geometric invariants of the manifold such as mean curvaturevolume etc. can be obtained from the asymptotic analysis of exit time of the Brownian motion from balls of small volume.It is therefore natural to explore the possibility of extending this philosophy to the quantum set-up, i.e. the possibility of connecting quantum stochastic calculus with non-commutative geometry (a la Connes), leading to a development of ‘quantum stochastic geometry’. As Brownian motions on manifolds are Markov processes with unbounded generators, it is important for pursuing this programme to have a reasonable theory of quantum stochastic calculus with unbounded coefficients. In this thesis, we shall begin by studying different aspects of quantum stochastic calculus with unbounded coefficients, and in the end, we shall try to connect the theory with non-commutative geometry.In chapter 1, we discuss the basic defintions and results e.g. C* and vonNeumann algebras, quantum isometry group, compact quantum group, quantum stochastic calculus, quantum dynamical semigroup, quantum stop-time etc, that we will be using in this thesis.The first difficulty in dealing with quantum stochastic calculus with unbounded coefficients is the absence of a convenient method for proving the homomorphic property of the quantum stochastic flow.


ProQuest Collection ID:

Control Number


Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.


Included in

Mathematics Commons