Alladi Ramakrishnan Hall

Effect of local quantum dynamical processes on spin chain dynamics

Saikat Sur

IIT-Kanpur

Quantum Information and communication aspect of quantum spin chains has been investigated over the last few years. From quantum information theory point of view, a quantum spin chain is a many­qubit system that can undergo various quantum dynamical processes (QDP), both global and local along with background unitary evolution. A local QDP that interrupts the background evolution can occur from a local quantum decohering process or local coherent operation.
We will focus on the possibility of detecting the signal from a QDP at farther sites from the dynamical evolution of the system for various spin models. We will also show that a local QDP can interfere with the background dynamics and change the distribution of correlations and entanglement structure like quantum state transfer fidelity.
Multiple incoherent QDPs intervening the dynamics at regular intervals can be thought of as if the system is interacting with an external decohering environment, while the action of multiple coherent QDPs though does not cause decoherence, can generate non­integrability in the system. We will discuss the behaviour of Loschmidt Echo, a measure of revival of a quantum state, to show a contrast between integrable and non integrable behaviour.
We will also make a connection between the dynamics of bipartite quantum correlations and quantum information scrambling by computing tripartite mutual information (TMI) in different spin systems. It has been observed that sharing of bipartite correlations implies a negative value of the TMI. We show that the bipartite correlations can be increased depending on the location and the time of the QDP occurrence and local QDPs can cause scrambling even when the background dynamics in non­scrambling in nature.

References:
1. Saikat Sur and V. Subrahmanyam, 'Quantum operations, information scrambling and redistribution of correlations through the dynamical evolution of spin chains', arXiv:1909.06056.
2. Saikat Sur and V. Subrahmanyam, 'Loschmidt Echo of local dynamical processes in integrable and non integrable spin chains', J phys. A. Math. Theor. 52 345301 (2019).
3. Saikat Sur and V. Subrahmanyam, 'Interference of the signal from a local dynamical process with a quantum state propagation in spin chains', J phys. A. Math. Theor. 52 015302 (2019).
4. Saikat Sur and V. Subrahmanyam, 'Remotely detecting the signal of a local decohering process in spin chains', J phys. A. Math. Theor. 50 205303 (2017).