2023-10-13 06:00:04
According to wave-particle duality, a quantum particle also behaves like a wave extended in space. Physicists have just observed the signature of two distinct properties of the same photon measured in two arms of an interferometer, separated by a few centimeters, thus illustrating the intrinsic delocalization of quantum objects.
Scheme of the experiment. A photon enters the interferometer from the bottom, propagates along arms A and B, then is detected at the exit of the interferometer (green check mark). The interactions in each arm are symbolized by the yellow wavy lines.
According to quantum theory, when a photon is sent into an interferometer everything happens as if the particle of light (Light is the set of electromagnetic waves visible to the eye…) propagated following the two arm of the interferometer at a time. Experimentally, this is generally seen following the fact, when we detect the photon at the exit of the interferometer, because the observed intensity shows interferences which sign the existence of these two paths taken by the particle.
On the other hand, understanding what is happening inside the interferometer remains a major challenge, because any measurement on the photon when it propagates in the interferometer irremediably disrupts it and destroys the interference pattern, for example when we seek to detect through which arm of the interferometer the photon passed.
In a new experiment carried out as part of a Franco-Indian collaboration including a researcher from the Theoretical Physics Laboratory (Theoretical physics is the branch of physics which studies the aspect…) and Modeling (LPTMCNRS / CY Cergy Paris Univ), an original approach was carried out by the joint and non-destructive measurement of two properties of the same photon during its evolution inside an interferometer, each property being measured in one of the arm of the interferometer.
The difficulty of the experiment is that it is necessary to preserve the coherence of the photon in the interferometer in order not to destroy the interference. The interaction must therefore be as weak as possible, while still producing measurable effects. The analogous experiments carried out so far might at best only implement a weak interaction in one of the arms, illustrating the difficulty of the undertaking.
In this new experiment, a single photon is sent into the interferometer. In one of the arms, an interaction with an optical component very slightly shifts the average position of the photon (or to be more precise, the spatial profile of its wave function) in a horizontal direction. This constitutes a non-destructive measurement of the presence of the photon in this arm of the interferometer. In the other arm of the interferometer, separated by a few centimeters, another optical component very slightly shifts the average position of the photon in a vertical direction (The vertical is a straight line parallel to the direction of gravity, given in particular by the. ..) (this is a non-destructive measurement of the polarization (the polarization of electromagnetic waves; the polarization due to moments, etc.) of the photon, the coupling of this component depending on the polarization of the photon). Finally, the photon leaves the interferometer and its position on a detector is measured in a plane.
By repeating the experiment several times, we observe that in the presence of interactions in each arm, the average position of the photon is displaced diagonally, reflecting both the displacement (In geometry, a displacement is a similarity which preserves the distances and angles…) horizontal (Horizontal is an orientation parallel to the horizon, and perpendicular to the…) due to the interaction horizontal in one arm and vertical in the other.
The displacement in each direction is proportional to what is called the “low value” of the measured physical quantity. The low values ​​measured experimentally during the experiment are in agreement with those predicted by quantum theory. This confirms that each photon jointly underwent the effect of simultaneous coupling in each arm. In the future, we will also be able, instead of using a property of the photon as a witness to the coupling, to use a different particle in each arm: the state quantum (In quantum mechanics, the state of a system describes all aspects of the physical system. It…) of each particle will then be modified by the corresponding weak value, even though these two particles are spatially separated. Such a diagram might have many applications in quantum technology. These results are published in the journal Communications Physics.
References
Unambiguous joint detection of spatially separated properties of a single photon in the two arms of an interferometer,
Surya Narayan Sahoo, Sanchari Chakraborti, Som Kanjilal, Saumya Ranjan Behera, Dipankar Home, Alex Matzkin et Urbasi Sinha, Communications Physics, published on 7 August 2023.
Doi: 10.1038/s42005-023-01317-7
Open archive: arXiv
1697185693
#photon #detected #analyzed #locations #time
