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Bohr EA, Kristensen SL, Hotter C, Schäffer SA, Robinson-Tait J, Thomsen JW, Zelevinsky T, Ritsch H, Müller JH. Collectively enhanced Ramsey readout by cavity sub- to superradiant transition. Nat Commun 2024; 15:1084. [PMID: 38316781 PMCID: PMC10844618 DOI: 10.1038/s41467-024-45420-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Accepted: 01/22/2024] [Indexed: 02/07/2024] Open
Abstract
When an inverted ensemble of atoms is tightly packed on the scale of its emission wavelength or when the atoms are collectively strongly coupled to a single cavity mode, their dipoles will align and decay rapidly via a superradiant burst. However, a spread-out dipole phase distribution theory predicts a required minimum threshold of atomic excitation for superradiance to occur. Here we experimentally confirm this predicted threshold for superradiant emission on a narrow optical transition when exciting the atoms transversely and show how to take advantage of the resulting sub- to superradiant transition. A π/2-pulse places the atoms in a subradiant state, protected from collective cavity decay, which we exploit during the free evolution period in a corresponding Ramsey pulse sequence. The final excited state population is read out via superradiant emission from the inverted atomic ensemble after a second π/2-pulse, and with minimal heating this allows for multiple Ramsey sequences within one experimental cycle. Our scheme is an innovative approach to atomic state readout characterized by its speed, simplicity, and highly directional emission of signal photons. It demonstrates the potential of sensors using collective effects in cavity-coupled quantum emitters.
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Affiliation(s)
- Eliot A Bohr
- Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen, DK-2100, Denmark.
| | - Sofus L Kristensen
- Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen, DK-2100, Denmark
| | - Christoph Hotter
- Institut für Theoretische Physik, Universität Innsbruck, Technikerstr. 21a, Innsbruck, A-6020, Austria
| | - Stefan A Schäffer
- Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen, DK-2100, Denmark
| | - Julian Robinson-Tait
- Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen, DK-2100, Denmark
| | - Jan W Thomsen
- Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen, DK-2100, Denmark
| | - Tanya Zelevinsky
- Department of Physics, Columbia University, 538 West 120th Street, New York, 10027-5255, NY, USA
| | - Helmut Ritsch
- Institut für Theoretische Physik, Universität Innsbruck, Technikerstr. 21a, Innsbruck, A-6020, Austria
| | - Jörg H Müller
- Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen, DK-2100, Denmark
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Troullinou C, Lucivero VG, Mitchell MW. Quantum-Enhanced Magnetometry at Optimal Number Density. PHYSICAL REVIEW LETTERS 2023; 131:133602. [PMID: 37831996 DOI: 10.1103/physrevlett.131.133602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 08/28/2023] [Indexed: 10/15/2023]
Abstract
We study the use of squeezed probe light and evasion of measurement backaction to enhance the sensitivity and measurement bandwidth of an optically pumped magnetometer (OPM) at sensitivity-optimal atom number density. By experimental observation, and in agreement with quantum noise modeling, a spin-exchange-limited OPM probed with off-resonance laser light is shown to have an optimal sensitivity determined by density-dependent quantum noise contributions. Application of squeezed probe light boosts the OPM sensitivity beyond this laser-light optimum, allowing the OPM to achieve sensitivities that it cannot reach with coherent-state probing at any density. The observed quantum sensitivity enhancement at optimal number density is enabled by measurement backaction evasion.
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Affiliation(s)
- Charikleia Troullinou
- ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain
| | - Vito Giovanni Lucivero
- ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain
- Dipartimento Interateneo di Fisica, Universitá degli Studi di Bari Aldo Moro, 70126 Bari, Italy
| | - Morgan W Mitchell
- ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain
- ICREA-Institució Catalana de Recerca i Estudis Avançats, 08010 Barcelona, Spain
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