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Deterministic Squeezed States with Collective Measurements and Feedback.

Kevin C Cox1, Graham P Greve1, Joshua M Weiner1

  • 1JILA, NIST, and University of Colorado, 440 UCB, Boulder, Colorado 80309, USA.

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Researchers created entangled, spin-squeezed atomic states using joint measurements and feedback. This quantum entanglement significantly improves measurement precision beyond the standard quantum limit for atomic ensembles.

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Area of Science:

  • Quantum physics
  • Atomic physics
  • Quantum optics

Background:

  • Standard quantum limit (SQL) restricts measurement precision.
  • Entanglement offers a path to surpass SQL.
  • Spin-squeezed states are crucial for enhanced quantum measurements.

Purpose of the Study:

  • To demonstrate the creation of entangled, spin-squeezed states using collective measurements and real-time feedback.
  • To deterministically drive atomic pseudospin states to specified population states.
  • To quantify the achievable improvement in quantum phase variance.

Main Methods:

  • Utilized a collective (joint) measurement on an ensemble of laser-cooled Rubidium-87 (⁸⁷Rb) atoms.
  • Implemented real-time feedback mechanisms to control the atomic state.
  • Measured the quantum phase variance relative to the standard quantum limit.

Main Results:

  • Achieved angular resolution 5.5(8) [7.4(6) dB] below SQL for N=5×10⁴ atoms using feedback.
  • Observed up to 59(8) times [17.7(6) dB] improvement in quantum phase variance without feedback for N=4×10⁵ atoms.
  • Demonstrated one of the largest reported entanglement enhancements in any system to date.

Conclusions:

  • Collective measurements and feedback enable significant entanglement-enhanced precision.
  • The demonstrated technique surpasses the standard quantum limit for atomic ensembles.
  • This work provides a powerful method for achieving high-precision quantum measurements.