arXiv subjects

Sneha Narasimha Moorthy

Publications and source records attributed to Sneha Narasimha Moorthy.

4 recordsLinked to original sources

arXiv2026

Random acceleration noise on Stern-Gerlach Interferometry in a Harmonic Trap

We analyze decoherence in a one-loop Stern--Gerlach--type matter-wave interferometer for a massive nanoparticle embedded with a nitrogen vacancy (NV)-centered nanodiamond evolving under an effective harmonic-oscillator dynamics in a magnetic-field gradient. We assume that the Stern-Gerlach interferometer is subjected to an acceleration $\vec{a}$ external to the system, which is at an angle $θ_0$ with respect to the direction of the superposition. For a one loop interferometer, we quantify dephasing from two noise channels: fluctuations in the external acceleration $δa(t)$ and fluctuations in the tilt angle $δθ(t)$. At the level of the action, we treat these two external noise as stochastic inputs, compute the resulting stochastic phase difference between the interferometer arms, and obtain the dephasing rate $Γ$. We obtain the transfer function of the interferometer for each of the noise sources. We also show explicit results of constraints on the power spectral density of the noise sources for an interferometer that produces a superposition size of $Δx\sim 1$nm of a nanodiamond of mass $m=10^{-15}~\mathrm{kg}$ by considering white noise statistics and imposing a coherence target $Γτ\leq 1$, where $τ\simeq 0.015~\mathrm{s}$. We find $\sqrt{\mathcal{S}_{aa}}\lesssim \mathcal{O}(10^{-11})~\mathrm{m\,s^{-2}\,Hz^{-1/2}}$ if we take the external acceleration, $a=0~{\rm ms^{-2}}$ and $θ_0=0^\circ$ (along the direction of the superposition), and $\sqrt{\mathcal{S}_{θθ}}\lesssim \mathcal{O}(10^{-10})~\mathrm{rad\,Hz^{-1/2}}$ for $a=g= 9.81~\mathrm{m\,s^{-2}}$ and $θ_0=90^\circ$ (superposition direction is perpendicular to the Earth's gravity). We have also found an operating regime where the acceleration noise can be minimized by either varying $θ_0$ or $a$ for a fixed set of other experimental parameters.

quant-ph↗

arXiv2026

Tunable Floquet selection rules in a driven Ising chain

We study a periodically driven spin-$1/2$ Ising chain with a nearest-neighbour coupling and longitudinal field while a weak transverse field induces single-spin flips. Through Floquet perturbation theory (FPT), we obtain signatures of Hilbert space fragmentation (HSF) and an unconventional form of dynamical localisation which we call the Floquet freezing. Our analysis suggests that these observations emerge due to a single Floquet selection rule that dictates the prethermal dynamics. For a special value of the field-to-interaction strength ratio together with commensurate drive periods, this rule permits only a constrained subset of bulk spin flips, leading to prethermal HSF in the full spin-$1/2$ Hilbert space. Under open boundary conditions, the same rule suppresses boundary spin flips up to higher order in perturbation and produces long-lived prethermal edge memory, which is neither topological in origin nor is a strong zero mode. Furthermore, under periodic boundary conditions, the largest surviving fragment is exactly the PXP sector at leading order and therefore exhibits Floquet-inherited scar phenomenology in the prethermal window. At higher commensurate ratios of field strength to interaction strength, all first-order single-spin-flip channels are suppressed and the system enters a regime of Floquet freezing. Hence, our study leverages the selection rules obtained through Floquet perturbation theory to obtain exotic prethermal phenomena at different parameter regimes.

cond-mat.other↗

arXiv2025

Magnetic noise in macroscopic quantum spatial superposition induced by inverted harmonic oscillator potential

We investigate a Stern-Gerlach type matter-wave interferometer where an inhomogeneous magnetic field couples to an embedded spin in a nanoparticle to create spatial superpositions. Employing a sequence of harmonic and inverted harmonic oscillator potentials created by external magnetic fields, we aim to enhance the one-dimensional superposition of a nanodiamond with mass $\sim 10^{-15}$ kg to $\sim 1 μ$m. However, random fluctuations of the magnetic field stochastically perturbs the interferometer paths and induce dephasing. We quantitatively estimate the susceptibility of the interferometer to white noise arising from magnetic-field fluctuations. Constraining the dephasing rate $Γ$ to be low enough that the final coherence $e^{-Γτ}\leq 0.1$ (where $τ$ is the experimental time duration), we obtain the following bounds on the noise to signal ratios: $δη_\text{IHP}/η_\text{IHP}\lesssim 10^{-13}$, where $η_\text{IHP}$ is the magnetic field curvature that gives rise to the inverted harmonic potential, and $δη_\text{HP}/η_\text{HP}\lesssim 10^{-6}$, where $η_\text{HP}$ is the linear magnetic field gradient that gives rise to the harmonic potential. For such tiny fluctuations, we demonstrate that the Humpty-Dumpty problem arising from a mismatch in position and momentum does not cause a loss in contrast of the interferometer. Further, we show that constraining the dephasing rate leads to stricter bounds on the noise parameters than enforcing a contrast threshold, indicating that good dephasing control ensures high interferometric contrast.

quant-ph↗

arXiv2025

Magnetic noise in macroscopic quantum spatial superposition

In this paper, we will show how random fluctuations in the magnetic field will jitter the paths of a matter-wave interferometer randomly, hence, decohere the quantum superposition. To create a large spatial superposition with nanoparticles, we envisage embedding a spin in a nanoparticle as a defect and applying an inhomogeneous magnetic field as in a Stern-Gerlach type experiment to create a macroscopic quantum superposition. Such matter-wave interferometers are the cornerstone for many new fundamental advancements in physics; particularly, adjacent matter-wave interferometers can use entanglement features to test physics beyond the Standard Model, test the equivalence principle, improve quantum sensors, and test the quantum nature of spacetime in a lab. In particular, we will use white and flicker noise to study the decoherence and constrain the parameters keeping in mind ambient temperatures suitable for superconducting wires embedded on a chip. We will show that to obtain a tiny spatial superposition of a nanometer separation, $Δx \sim {\cal O} (10^{-9})$m and to minimize decoherence, $Γ\leq {\cal O}(\frac{ω_0}{2π})$, where $Γ$ is the decoherence and $ω_0$ is the frequency of the oscillator, we will need current fluctuations to be $δI/I\leq {\cal O}(10^{-8})$, which is not impossible to obtain in superconducting wire arrangements. For such tiny fluctuations, we demonstrate that the Humpty-Dumpty problem in a matter-wave interferometer arising from a mismatch in position and momentum does not cause a loss in contrast.

quant-ph↗