Observing the average trajectories of single photons in a two-slit interferometer

Area of Science:

• Quantum mechanics
• Quantum optics
• Interferometry

Background:

• The Heisenberg uncertainty principle fundamentally limits simultaneous precise measurements of a quantum particle's position and momentum.
• Directly observing a quantum particle's trajectory is precluded by measurement back-action.

Purpose of the Study:

• To operationally define and observe quantum particle trajectories using weak measurements.
• To provide an observationally grounded description of quantum particle propagation in a two-slit interferometer.

Main Methods:

• Single photons from a quantum dot were sent through a double-slit interferometer.
• Weak measurements of photon momentum were performed.
• Postselection based on strong measurements of photon position in successive planes allowed trajectory reconstruction.

Main Results:

• Reconstructed trajectories for ensembles of single photons were obtained.
• The study demonstrated the feasibility of defining and observing quantum trajectories.

Conclusions:

• Weak measurements offer a method to circumvent the limitations imposed by the uncertainty principle for trajectory observation.
• This technique provides a novel way to study the propagation of quantum particles in interferometric setups.