arXiv subjects

Bidhi Vijaywargia

Publications and source records attributed to Bidhi Vijaywargia.

3 recordsLinked to original sources

arXiv2026

Instability-Enhanced Quantum Sensing with Tunable Multibody Interactions

Dynamical instabilities can amplify small perturbations into measurable signals, offering a route to quantum-enhanced sensing. This mechanism was experimentally demonstrated in a collective-spin system with quadratic interactions, described by a twisting-and-turning Hamiltonian, where quantum evolution near an unstable point leads to exponential growth of spin fluctuations, enabling metrological gain beyond the standard quantum limit. Here, we show that a quartic extension of this Hamiltonian substantially increases the amplification. The additional nonlinear term reshapes the phase-space structure, generating new unstable points and accelerating signal amplification. As a result, enhanced sensitivity is achieved within experimentally accessible coherence times. Remarkably, even at fixed instability rate (equal Lyapunov exponent), multibody interactions outperform the quadratic case due to enhanced short-time dynamics. We analyze the classical and quantum behavior of the multibody model and discuss its experimental implementations. Our results identify phase-space curvature as a resource for optimizing the speed and performance of quantum sensors.

quant-ph↗

arXiv2026

Universal spectral correlations in open Floquet systems with localized leaks

We show that introducing a localized leak in Floquet systems with time-reversal symmetry leads to universal spectral correlations governed by the non-Hermitian symmetry class $\mathrm{AI}^{\dagger}$, associated with complex-symmetric Ginibre random matrices, rather than by the unconstrained Ginibre ensemble. As a concrete example, we analyze the leaky quantum standard map (L-QSM) of the kicked rotor. Since the closed map exhibits circular orthogonal ensemble (COE) statistics, the open system is naturally compared with the truncated circular orthogonal ensemble (TCOE), which models localized leakage by removing columns from a COE matrix. We find excellent agreement between the bulk spectral properties of the L-QSM and the TCOE, and demonstrate that their short-range spectral correlations follow the universal statistics of the non-Hermitian symmetry class $\mathrm{AI}^{\dagger}$. This agreement holds for smaller leak sizes as the matrices increase, while the COE limit is recovered only when the truncation is smaller than one full column. In contrast to local properties, the global density of states of the L-QSM and the TCOE approaches the Ginibre circular law only when the leakage becomes sufficiently strong.

cond-mat.stat-mech↗

arXiv2024

Quantum-classical correspondence in quantum channels

Quantum channels describe subsystem or open system evolution. Using the classical Koopman operator that evolves functions on phase space, 4 classical Koopman channels are identified that are analogs of the 4 possible quantum channels in a bipartite setting. Thus when the complete evolution has a quantum-classical correspondence the correspondence at the level of the subunitary channels can be studied. The channels, both classical and quantum can be interpreted as noisy single particle systems. Having parallel classical and quantum operators gives us new access to study fine details of these major limiting theories. Using a coupled kicked rotor as a generic example, we contrast and compare spectra of the quantum and classical channel. The largest nontrivial mode of the quantum channel is seen to be mostly determined by the stable parts of the classical phase space, even those that are surprisingly small in relation to the scale of an effective $\hbar$. In the case when the dynamics has a significant fraction of chaos the spectrum has a prominent annular density that is approximately described by the single-ring theorem of random matrix theory, and the ring shrinks in size when the classical limit is approached. However, the eigenvalues and modes that survive the classical limit seem to be either scarred by unstable manifolds or, if they exist, stable periodic orbits.

quant-ph↗