its momentum uncertainty is comparable to that of a single photon.
https://journals.aps.org/prl/abstract/10.1103/93zb-lws3
By varying the trap depth of the optical tweezer, we dynamically tune the atom’s intrinsic momentum uncertainty, thus enabling the observation of a gradual shift in the visibility of single-photon interference.
https://arxiv.org/pdf/2410.10664
For a ground-state atom in a harmonic potential, the momentum uncertainty is intricately
linked to the phonon frequency, which in turn depends on the trap depth, following a
fourth-root dependence....This makes the atom an ideal quantum beam-splitter envisioned by Einstein.
this broader momentum wavefunction leads to a greater degree of overlap after being displaced by the recoil momentum from a single photon, ....the observed reduction of the visibility in Fig. 4b at increasing 𝑛̄ [phonon] agrees well with the theoretical prediction, which clearly shows the difference between quantum and classical effect on the interference visibility.
the Einstein-Bohr interference visibility is determined by the degree of quantum entanglement in the momentum degree of freedom between the photon and the slit.
AI says:
precisely measuring a photon's path (via recoil) destroys its interference pattern, with tunability allowing observation of the transition from wave to particle behavior by altering the atom's momentum uncertainty...Niels Bohr countered that precisely measuring the slit's momentum (its recoil) would, due to the Heisenberg Uncertainty Principle, introduce enough position uncertainty to wash out the interference pattern, upholding complementarity....
atom's momentum path] uncertainty was high (loose trap), the photon showed wave-like interference [position]; when the trap was tightened, revealing the [momentum] path, the interference visibility [position] decreased, demonstrating the quantum-classical transition and validating Bohr's argument
because only one atom and one photon is used the tuning could precisely determine the switch from entanglement [fringe position] to a particle [momentum path].
https://physics.aps.org/articles/v18/s150
a precise measurement of a particle’s momentum [path] would, thanks to the uncertainty principle, blur the particle’s position and wash out the fringes [entangled position]. Bohr argued that quantum objects possess complementary properties, such as being a particle (with a definite path) and a wave (producing an interference pattern), but that these properties cannot be observed simultaneously. The very act of measurement, Bohr claimed, forces the object into one state or the other.
By tuning the photons’ momentum uncertainty, Pan and his collaborators could make the fringes more or less blurry, in line with theory.
https://english.cas.cn/newsroom/cas_media/202512/t20251208_1135579.shtml
For decades, Einstein's challenge remained a theoretical puzzle. The USTC team has now turned it into a physical reality. They constructed an advanced apparatus of extreme sensitivity, capable of detecting the minuscule momentum transfer of a single photon.
Conversely, observing the clear interference pattern necessitates abandoning all information about the individual particle's [momentum] path.
This finding underscores a fundamental limit to measurement and observation inherent in the quantum world – a limit Bohr embraced
the paradoxical behavior of quantum particles is not due to experimental shortcomings but is a core feature of reality itself.
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