New Type of Quantum Entanglement Demonstrated
Physicists at the Technion – Israel Institute of Technology say they have observed a new form of quantum entanglement in the total angular momentum of photons confined in nanoscale structures. Their work paves the way for on-chip quantum information processing using the total angular momentum of photons as the encoding property for quantum information.
Conversion occurring in a nanometric system of two photons into an entangled state in their total angular momentum. Image credit: Shalom Buberman, Shultzo3d.
Quantum entanglement has been demonstrated so far for a wide variety of particles and for their various properties.
For photons, particles of light, entanglement can exist for their direction of travel, frequency, or the direction in which their electric field points.
It can also exist for properties that are harder to imagine, such as angular momentum.
This property is divided into spin, which is related to the photon’s rotation of the electric field, and orbit, which is related to the photon’s rotational motion in space.
“It is easy for us to imagine these two rotational properties as separate quantities, and indeed, photons bound in a beam of light much wider than their wavelength,” said Professor Guy Bartal and colleagues in a statement.
“However, when we try to put photons into structures smaller than the photonic wavelength — which is the endeavor of the field of nanophotonics — we discover that it is impossible to separate the different rotational properties, and the photon is characterized by a single quantity, the total angular momentum.”
“So why would we even want to put photons into such small structures? There are two main reasons for this.”
“One is obvious — it will help us to miniaturize devices that use light and thus squeeze more operations into a small area cell, similar to the miniaturization of electronic circuits.”
“The other reason is even more important: this miniaturization increases the interaction between the photon and the material through which the photon is traveling (or is near), thus allowing us to produce phenomena and uses that are not possible with photons in their ‘normal’ dimensions.”
In their new study, the researchers discovered that it is possible to entangle photons in nanoscale systems that are a thousandth the size of a hair, but the entanglement is not carried out by the conventional properties of the photon, such as spin or trajectory, but only by the total angular momentum.
They revealed the process that photons undergo from the stage in which they are introduced into the nanoscale system until they exit the measurement system, and found that this transition enriches the space of states that the photons can reside in.
In a series of measurements, they mapped those states, entangled them with the same property unique to nanoscale systems, and confirmed the correspondence between photon pairs that indicates quantum entanglement.
“This is the first discovery of a new quantum entanglement in more than 20 years, and it may lead in the future to the development of new tools for the design of photon-based quantum communication and computing components, as well as to their significant miniaturization,” the scientists concluded.
Their paper was published in the journal Nature.
