03/26/2026
By Rohan Garlapad

The Kennedy College of Sciences, Department of Physics and Applied Physics, invites you to attend a Master’s thesis defense by Rohan Garlapad on “Optimum Measurement Quadrature for Frequency Estimation of Spin-Squeezed States.”

Candidate: Rohan Garlapad
Degree: Master’s in Physics
Defense Date: Friday, April 3, 2026
Time: 3:30 to 5 p.m.
Location: Olney Science Center 430, North Campus
Thesis Title: Optimum Measurement Quadrature for Frequency Estimation of Spin-Squeezed States

Committee:

  • Advisor: Hugo Ribeiro Ph.D., Department of Physics and Applied Physics, University of Massachusetts Lowell
  • Viktor A Podolskiy Ph.D., Department of Physics and Applied Physics, University of Massachusetts Lowell
  • Peter Bender Ph.D., Department of Physics and Applied Physics, University of Massachusetts Lowell

Brief Abstract:
Quantum sensing is an emergent field that explores how quantum resources, e.g., entanglement and non-classical states like spin-squeezed states, can enhance the measurement of physical quantities, including magnetic fields and related observables. The central aim is to design measurement protocols that surpass the sensitivity limits imposed by the Standard Quantum Limit (SQL) and achieve high precision. In this context, a single qubit is often treated as a “classical” sensor, since superposition states can be effectively reproduced in systems governed by classical physics—for instance, coupled harmonic oscillators. The most established sensing technique is Ramsey interferometry, which enables the estimation of an unknown frequency. More recently, an Iterative Adaptive Sensing (IAS) protocol based on Ramsey interferometry has been introduced to address several limitations inherent to standard Ramsey measurements. A key advantage of IAS is its ability to accurately determine an unknown frequency even when only a short signal is available.

This work explores how incorporating spin-squeezed states can further enhance the precision of atomic interferometry. We show that, despite the presence of noise, a Ramsey-type protocol employing spin-squeezed states can generate measurement signals that allow high-precision frequency estimation. The estimation procedure relies on identifying an optimal measurement quadrature that reduces the relative error in the frequency estimate.

In our study, we analyzed the power spectrum obtained from the Fourier transform of the generalized spin operator of spin-squeezed states to identify an optimal measurement direction that reduces the relative error in the frequency estimate. Our findings indicate the existence of an optimal measurement direction that substantially reduces the relative error in the frequency estimate even in the presence of local Markovian dissipation.