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“Unlocking” spin-valley locked Kramers qubit states

Bhaskaran Muralidharan (Department of Electrical Engineering, IIT Bombay, Mumbai, India)

Abstract: There is growing interest in the physics of zero-dimensional quantum states in 2D semiconductor with hexagonal lattices such as bilayer graphene (BLG) and Transitional metal dichalcogenides (TMDC). Spin-valley coupling in such heterostructures canspecifically result in Kramers degeneracy, which can “lock” time-reversal symmetry protected states. These states form the basis of what is known as the Kramers qubit, which thereby promises very long relaxation times. In this talk, we will delve into our generalized strategy [1-3] to understand a wide variety of experiments under diverse conditions through a unified theoretical framework. With the insights gained, we reveal the operating conditions based on intrinsic properties and extrinsic factors the ideal conditions of operating spin-valley qubits.

Moving on to the lifetimes of the spin-valley qubits, we provide a consistent interpretation of recent [4] comprehensive single shot readout measurements. By integrating theoretical predictions of pure state lifetimes with multi-state dynamics of the readout process, we bring to the fore the role of protocol-induced extrinsic factors that redistribute relaxation pathways near spin-valley qubit operating points, leading to lifetime estimates different from T1. With this missing link, we propose new interpretation of the measured lifetime trends in magnetic field and as well as comment on the applicability of a generalized Mathiessen’s rule around the level anti-crossings.

We conclude by providing an outlook on how quantum transport modeling can be seamlessly employed to understand current topics that include spintronics and superconducting hybrid systems [5,6]. In doing so, we also provide our perspectives on what quantum transport-based device modeling needs to incorporate in order to transition toward an all-encompassing platform in the near future.

[1]  A. Mukherjee and B. Muralidharan, 2D Materials, 10, 035006, (2023). 

[2].   A. Mukherjee, A. Das, A. Khan and B. Muralidharan, APL Quantum, 2, 026125, (2025). 

[3]   A. Shandilya, S. Kapila, et. al., ACS Appl. Nano. Mat., 8, 14949, (2025). 

[4]   A O Denisov et al., Nat. Nano.,20, 494, (2025). 

[5]   R. Singh and B. Muralidharan, Comms Phys., 6, 36,(2023). 

[6]   A. Arora, S. Midha et.al., npj Quantum Inf., 11, 40 (2025).