OSC Colloquium: Morgan Mitchell

“How well does quantum mechanics allow us to know the magnetic field?”


3:30 to 5 p.m., Feb. 9, 2023


Title: “How well does quantum mechanics allow us to know the magnetic field?”


Precise measurement of magnetic fields is important to many scientific and technical fields, from brain imaging to space science. A great many magnetometer technologies have been developed for these many applications, and a great deal of effort has been put into improving their sensitivity. Curiously, completely different magnetometer technologies arrive to a similar limiting sensitivity, once magnetometer size is taken into account: larger magnetometers are more sensitive, but if you replaced a large magnetometer with many small magnetometers, you would break even. Still more curiously, it is known for dc-SQUIDs (superconducting devices), rubidium optically-pumped magnetometers, and nitrogen-vacancy centers in diamond, that this limiting sensitivity (in appropriate units) is hbar, the quantum of action. This suggests that there might be some as-yet-undiscovered quantum limit to field sensing. If such a limit exists, it would be a qualitatively different limit from other, better-known limits such as the standard quantum limit and the so-called “Heisenberg limit.” I will discuss our hunt for this mysterious limit, as well as our efforts to surpass the hbar limit using a spinor Bose-Einstein condensate as an extreme field sensor.


Dr. Morgan Mitchell,
Group Leader - Atomic Quantum Optics Research Group
ICFO, Barcelona Spain

Prof. Mitchell leads the Atomic Quantum Optics research group at The Institute of Photonic Sciences (ICFO) in Barcelona, Spain, and holds the title of ICREA Research Professor. He has applied quantum optics to a number of quantum technologies, including quantum sensing, quantum communications, and quantum random number generation, as well as to quantum foundations topics such quantum non-locality. His quantum sensing activities largely focus on extreme sensing of magnetic fields and include the first application of squeezed light to magnetic sensing, the first application of spin squeezed states to magnetic sensing, and the invention of new spin-squeezing protocols that escape quantum measurement back-action. He developed the quantum random number generators used in the loophole-free Bell tests of 2015, one of which was recently recognized with the Nobel Prize in Physics, and in 2017 he co-founded Quside Technologies, a company that commercializes quantum random number generators. He was awarded an ERC Starting Grant in 2011, an ERC Proof-of-Concept Grant in 2016, and has been recognized with a Vanguardia de la Ciencia award in 2012, Ehrenfest Prize and Kavli Publication Prize in 2016.


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