Squeezing and over-squeezing of triphotons

Area of Science:

• Quantum Optics
• Quantum Information Science
• Metrology

Background:

• Quantum mechanics defines a standard quantum limit for measurement accuracy, with uncertainty typically shared between complementary properties.
• Spin squeezing, a technique to reduce uncertainty in one property below this limit, is crucial for quantum light-matter interfaces but has been far from the theoretical Heisenberg limit.
• Existing optical spin-squeezed systems have shown progress but remain orders of magnitude below the maximum achievable squeezing.

Purpose of the Study:

• To demonstrate optical spin squeezing approaching the fundamental Heisenberg uncertainty limit.
• To explore the creation and properties of spin-squeezed states using few-photon systems.
• To investigate the role of spherical topology in limiting squeezing and the phenomenon of 'over-squeezing'.

Main Methods:

• Generation of spin-squeezed states by overlapping three indistinguishable photons in an optical fiber.
• Manipulation of photon polarization (spin) to form a 'triphoton', a squeezed composite particle.
• Characterization of triphoton states using quasi-probability distributions on a spherical surface.

Main Results:

• Demonstrated optical spin squeezing that reaches essentially the fundamental Heisenberg uncertainty limit.
• Observed 'over-squeezing' where quasi-probability distributions wrap around the sphere due to polarization's spherical topology.
• Successfully created and characterized spin-squeezed states in the few-photon regime.

Conclusions:

• The developed optical system allows for spin squeezing close to the theoretical maximum, overcoming previous limitations.
• The findings highlight the impact of spherical topology on quantum squeezing and introduce the concept of 'over-squeezing'.
• This work paves the way for new quantum resources for enhanced measurement, lithography, and information processing engineered at the photon level.