Optical phase estimation approaching the quantum limit in a single shotOptical phase estimation approaching the quantum limit in a single shot

Optical phase estimation approaching the quantum limit in a single shot

Optical phase estimation is at the center of many metrological tasks where the value of a physical parameter of a system is mapped to the phase of an electromagnetic field, and single-shot measurements of this phase retrieve the information of this parameter. In this article, we demonstrate optimized estimation strategies for single-shot measurements for the optical phase of coherent states, which achieve sensitivities surpassing the heterodyne limit and potentially approaching the quantum limit, the Cramer-Rao lower bound (CRLB). These strategies are based on optimized photon counting, coherent displacement operations, and fast feedback. Our demonstration uses fast processing for optimizing the single-shot measurement during the optical mode, and enables surpassing the heterodyne limit for a wide range of optical powers without correcting for detection efficiency of our system. This is, to our knowledge, the most sensitive single-shot measurement of an unknown phase encoded in optical coherent states

This research has been published in Physical Review Letters, and can be accessed in https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.120505

Optical phase estimation approaching the quantum limit in a single shot

(a) The input state and optimized local oscillator (LO) interfere on a beam splitter such that the input is displaced in phase space. The probability distribution for the unknown phase is then updated according to Bayes rule and new optimal values for the LO are applied. (b) Experimental data (points with error bars) shows that adaptive non-Gaussian measurements surpass the limits of ideal heterodyne detection (dashed red) and approach the fundamental sensitivity limit given by the CRLB for our detection efficiency of 70% (solid black)

CQuIC Welcomes Postdoctoral Fellow, Tzula Propp to CQuIC

CQuIC welcomes Dr. Tzula Propp as a Postdoctoral Fellow.   Recently, Tzula completed their PhD in Quantum Information Theory at the University of Oregon where they worked with Steven van Enk exploring the fundamental limits and trade-offs intrinsic to the detection of single photons. Along the way, they developed expertise in quantum measurement theory and quantum optics. Here at CQuIC, Tzula is excited to continue and apply this work to the study of Quantum Key Distribution, as well as deepen their understanding of quantum measurement. Once in Albuquerque, Tzula looks forward to mentoring PhD students, enjoying the sights and tastes of Albuquerque, and those chance hallway conversations that lead to the best research collaborations and friendships.  

Four CQuIC Faculty Receive EAGER Awards

EArly-concept Grants for Exploratory Research (EAGER) are awarded by the National Science Foundation (NSF) each year to support exploratory work in its early stages on untested, but potentially transformative, research ideas or approaches. This work may be considered especially “high risk-high payoff” in the sense that it, for example, involves radically different approaches, applies new expertise, or engages novel disciplinary or interdisciplinary perspectives.

CQuIC is proud to announce that this year, four CQuIC faculty received EAGER awards. Professors Akimasa Miyake, Elizabeth Crosson, and Tameem Albash have been awarded grants under the Quantum Algorithm Challenge, the largest number of such grants awarded to any institution this year.  Professor  F. Elohim Becerra Chavez was awarded an EAGER grant from the Division of Molecular and Cellular Biology, jointly with Prof. Keith Lidke of the Department of Physics & Astronomy and Prof. Diane Lidke of the Department of Pathology in the School of Medicine.  The work of the faculty and their research groups funded by the EAGER awards will enhance other current and future projects in quantum information science conducted at CQuIC and collaboratively across campus.

With the aid of NSF EAGER award, Miyake group aims to apply explicitly correlated electronic structure theory in quantum chemistry to quantum algorithms and simulation. This new project is also synergetic with ongoing NSF-funded STAQ quantum computing project, which co-designs state-of-the-art ion-trap quantum computers for practical applications.

Crosson’s project investigates the connection between physical thermalization – the process by which a physical quantum system comes into thermal equilibrium with its environment – and the behavior and convergence of quantum algorithms for simulating thermal states.   Specifically, the project investigates the quantum Metropolis algorithm, which is a quantum algorithm that directly generalizes one of the most successful 20th century paradigms for simulating classical statistical physics.   By paralleling developments that occurred in the corresponding classical algorithm, this project seeks to determine general conditions which imply that a quantum computer can efficiently simulate quantum thermal properties.

The research goal of the Albash group is to use the EAGER award to study the viability of hybrid quantum-classical algorithms to deliver a quantum advantage for approximating the ground state of many-body non-stoquastic Hamiltonians, a class of quantum Hamiltonians that describes many relevant model systems.  This project will make this assessment by combining lessons from spin-glass theory and a side-by-side comparison of the computational cost of hybrid quantum-classical variational algorithms and state-of-the-art classical algorithms using well-defined problem classes of non-stoquastic Hamiltonians of varying difficulty. The project highlights the multi-disciplinary nature of quantum computing and will train students to have a diverse toolbox to tackle emerging challenges in the field.

The collaboration among the groups of Becerra, K. Lidke, and D. Lidke is an interdisciplinary effort in cell biology and biophysics; single-molecule super-resolution microscopy; and quantum optical measurements. This work investigates the use of quantum-enhanced measurements for approaching the physical limits in precision in localization to study protein-protein interactions and determine protein organization during cellular signaling. Such knowledge will provide a fundamental understanding of how changes in membrane protein organization govern cellular outcome, both in normal and diseased states.


Dynamical Phase Transitions

Using measurement and feedback control to simulate complex mean field spin dynamics in quantum systems

In physical systems composed of many parts, like ultracold atomic ensembles, electrons in a superconductor, or arrays of superconducting circuits, complex dynamics emerges when the different parts of the system interact with each other. Even though typical low-energy interactions found in nature are of two-body nature, considering higher order interactions can lead to novel complex phenomena which could be studied in quantum simulators. In fact, achieving programmable simulation of many-body interactions is a central goal of near-term quantum information processing devices.

Recent work from CQuIC led by PhD student Manuel Muñoz-Arias and FRHTP postdoc Pablo Poggi together with Professors Poul Jessen and Ivan Deutsch, demonstrated the viability of combining quantum measurements and feedback control to program the simulation of a family of spin systems called “p-spin models” which exhibit complex nonlinear dynamics related to the mean-field interaction of p bodies. [1].  In particular it was shown how this simulation scheme can be used to investigate the emergence of phenomena such as dynamical phase transitions, which are drastic changes on the macroscopic motion of a system as a single parameter is varied, and spontaneous symmetry breaking in adiabatic evolution induced by measurement. The proposal is particularly suited to explore such signatures of critical phenomena in simple systems such as ensembles of utlracold atoms subject to global measurements and control. The work gives a fresh twist to the well-established toolbox of quantum feedback control, previously studied in quantum optics, and extend this tool to explore a broad scope of physical phenomena.

This research has been published in Physical Review A, and can be accessed in https://journals.aps.org/pra/abstract/10.1103/PhysRevA.102.022610

Dynamical Phase Transitions
Simulation of dynamical phase transitions in the mean field dynamics using quantum measurements and feedback (black and orange symbols). (a) and (c) show long-time average magnetization as a function of the external field. Sharp change indicates the phase transition. (b) and (d) show the same feature for a long-time average expectation value of a two-body operator. Results are to be comparead with the exact mean-field solution (solid red line)

[1] Manuel H. Muñoz-Arias, Ivan Deutsch, Poul Jessen, Pablo Poggi, “Simulation of the complex dynamics of mean-field p-spin models using measurement-based quantum feedback control”, Phys. Rev. A 102, 022610 (2020)