My broad area of research is quantum information theory, with occasional ventures in quantum many-body physics, quantum thermodynamics, and open quantum systems, mainly to explore their connections with quantum information protocols. The areas that I am currently exploring are the following.

1. Designing  efficient protocols to quantify and compute "local" entanglement in noisy topological quantum codes

2. Thermodynamics of quantum error correction 

3. Quantum tasks using logical qubits

4. How to deal with noisy measurements in quantum protocols?

5. Quantum games on noisy quantum systems

Some of my recent works in these directions are as follows. 

Deterministic entanglement concentration assisted by graph state basis

Collaborator: Harikrishnan K. J.

We design effectively deterministic  protocol for concentrating bipartite entanglement over a two-qubit system from arbitrary number of two-qubit weakly-entangled pure states via a truncation of the Hilbert space corresponding to a multi-qubit subsystem to a single-qubit Hilbert space. This truncation is achieved via a multi-qubit measurement in the  graph state basis, which is equivalent to a repetitive two-qubit measurement protocol, where the measurements on the multi-qubit subsystem is performed taking pairs of qubits at a time, and concentration of entanglement is possible in each round of two-qubit measurements. We derive lower and upper bounds of the entanglement concentrated after a given number of rounds of measurements, where the entanglement of the initial weakly-entangled two-qubit systems are not-necessarily equal, and apply the protocol to create generalized GHZ states on arbitrary number of qubits, thereby underlining the possibility of creating maximally entangled qubit pairs via qubit-local projection measurements. To learn about the details of our protocol, see arXiv:2410.15892.

In the strong rung-coupling limit, the isotropic Heisenberg model in a magnetic field on a two-dimensional rectangular zig-zag lattice of arbitrary size can be mapped to a 1D effective model representing the low-energy manifold of the 2D model up to second order in perturbation theory, as we demonstrate in Phys. Rev. A. 110, 032408 (2024) . We exploit this to transfer low-energy multi-qubit rung states on a quasi-1D lattice, where each rung behaves as a "logical" qubit, and the time evolutions involved in the state transfer protocol are generated by the effective 1D Hamiltonian.  We propose protocols for transferring arbitrary single-qubit states from one lattice site to another by using specific encoding of the single-qubit state into a low-energy rung state, and a subsequent decoding of the transferred state on the receiver rung. These encoding and decoding protocols involve a time evolution generated by the 1D rung Hamiltonian and single-qubit phase gates, ensuring that all time-evolutions required for transferring the single-qubit state are generated from 1D Hamiltonians. The performance of the single-qubit state transfer using the proposed protocol is always better than the same when a time-evolution generated by the full quasi-1D Hamiltonian is used. To know more about this protocol, see Phys. Lett. A 511, 129543 (2024).

Localizable entanglement in noisy topological quantum codes

Collaborators: Harikrishnan KJ, David Amaro, Markus Müller

Topological quantum error correcting codes, including the Kitaev code and the color code, have emerged as leading candidates towards the goal of achieving large-scale fault-tolerant quantum computers. These systems are realized by arranging qubits on lattices of specific geometry, and are robust against external perturbation, qubit loss, and computational errors. These systems have also been implemented in the laboratory with, for example, trapped ions, and superconducting qubits. It is now clear that in order to host a single logical qubit with low or moderate code distance, and to perform error correction protocols taking into account errors on multiple physical qubits, one needs to deal with systems with a large number of physical qubits in the presence of noise. This makes the investigation of these systems difficult both in the theoretical and experimental fronts. 

Our research aims to explore two directions: 

1. Developing computable protocols for calculating localizable entanglement in these systems with an experimentally relevant fashion: Towads this, we have designed a graph-based technique for computing localizable entanglement over arbitrary subsections of topological quantum codes of arbitrary sizes, and an interpretation of the same via local entanglement witness operators to make the estimation of entanglement experimentally accessible. To learn about it, see Phys. Rev. A 108, 032404 (2023), New J. Phys. 22, 053038 (2020), and New. J. Phys. 20, 063017 (2018).

2. Exploring effects of external perturbations such as local magnetic fields, spin-spin interactions, and disorder in these systems using the developed approach. In this direction, we explore the topological-to-non-topological quantum phase transitions in the topological quantum codes in the present of "local" perturbations. See Phys. Rev. A. 111, 032401 (2025), and Phys. Rev. A 105, 052421 (2022).