EQUS seminar series: Matt Goh

Speaker: Matt Goh

Title: Controlling the demon condensate: feedback cooling of atomic Bose gases

Abstract: Current methods for producing Bose–Einstein condensates mostly rely on evaporative cooling for their final stage, resulting in the loss of more than 99.9% of atoms in the trap. In this talk, I outline current theoretical investigations into the viability of feedback cooling, a proposed low-loss method of cooling atomic Bose gases to a high condensate fraction via closed-loop controls. I present results from recent simulations demonstrating that the technique can cool a quasi-1D 'cigar' condensate from 5% initial condensate fraction to over 90%. I account for the effect of various experimental imperfections such as the resolution of optical control potentials, time delays in the feedback loop, quantum efficiency of the detector, and corrupting noise in the measurement channels. I demonstrate that feedback cooling can successfully operate within realistic experimental constraints, and conclude that it is a viable alternative to evaporative cooling. Following this, I present a technical discussion of the theory powering these simulations, outlining the use of a projective form of the number-phase-Wigner phase-space particle filter to simulate beyond-mean-field dynamics of Bose–Einstein condensates under continuous measurement at finite temperature.

Bio: Matt Goh completed Honours in Physics in 2019 at the Australian National University, graduating with First Class Honours, the University Medal, and the John Carver Physics Prize. In his time at the ANU from 2019 to 2021, he has worked in the Quantum Optics and Quantum Many-Body Systems Group, conducting research into novel closed-loop control methods for ultracold atoms. He has additionally worked in other groups, including the Nir Davidson Lab at the Weizmann Institute of Science, and the Condensed Matter Theory Group at the University of Oxford. He currently works as a Quantum Control Engineer at Q-CTRL. Matt has been selected as a Rhodes Scholar and will return to Oxford to complete a PhD with the Quantum Technology Theory Group.

Many thanks to Tim Harris for organising.

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Major funding support

Australian Research Council

The Australian Research Council Centre of Excellence for Engineered Quantum Systems (EQUS) acknowledges the Traditional Owners of Country throughout Australia and their continuing connection to lands, waters and communities. We pay our respects to Aboriginal and Torres Strait Islander cultures and to Elders past and present.