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Photon Connection Helps Researchers Entangle Large, Distant Objects

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Disparate, Entangled Objects Hold Promise for Next-Level Quantum Mechanics

KØBENHAVN, Denmark, Oct. 12, 2020 — Researchers at the Niels Bohr Institute at the University of Copenhagen have entangled two very different quantum objects — a mechanical oscillator/vibrating dielectric membrane, and a cloud of atoms with each atom acting as a tiny magnet. In addition to wholly disparate, the objects are much larger than classically entangled object pairs, giving the development potential applications in ultraprecise sensing and quantum communications.

The objects acquired the ability to be entangled by physically connecting with photons. As photons moved between the two objects, a correlation formed, linking the motion of the objects. The correlated motion of the entangled objects present a precision better than the zero-point motion — the residual uncorrelated motion of all matter that occurs even at absolute zero.

As individual components, atoms are useful in processing quantum information. The membrane — and mechanical quantum systems in general — are useful in storing quantum information.

Quantum mechanics is like a double-edged sword. It gives us wonderful new technologies, but also limits precision of measurements which would seem just easy from a classical point of view,” said research team member Michal Parniak.

Entangled systems can remain perfectly correlated even when positioned at a distance from each other. This dynamic has puzzled researchers since the beginning of the study of quantum mechanics more than 100 years ago.

“The bigger the objects, the farther apart they are, the more disparate they are, the more interesting entanglement becomes from both fundamental and applied perspectives,” said Eugene Polzik, professor of physics at the Niels Bohr Institute.


Light propagates through the atomic cloud shown in the center and then falls onto the SiN membrane shown on the left. As a result of interaction with light the precession of atomic spins and vibration of the membrane become quantum correlated. This is the essence of entanglement between the atoms and the membrane. Courtesy of Niels Bohr Institute.
Light propagates through the atomic cloud shown in the center and then falls onto the SiN membrane shown on the left. As a result of interaction with light the precession of atomic spins and vibration of the membrane become quantum correlated. This is the essence of entanglement between the atoms and the membrane. Courtesy of Niels Bohr Institute.
The technique has potential for sensing in oscillators of any size. The Laser Interferometer Gravitational-Wave Observatory (LIGO) senses and measures extremely faint waves caused by astronomical events in deep space. The waves shake the mirrors of the interferometer, which allows them to be sensed, though the sensitivity is limited by quantum mechanics as the mirrors are also shaken by zero-point fluctuations.

In principle, it is possible to generate entanglement of the LIGO mirrors with an atomic cloud and thus cancel the zero-point noise of the mirrors in the same way as the membrane in the research team’s experiment. The researchers are working on a model experiment demonstrating that principle.

The research was published in Nature Physics (www.doi.org/10.1038/s41567-020-1031-5).


Published: October 2020
Glossary
quantum
The term quantum refers to the fundamental unit or discrete amount of a physical quantity involved in interactions at the atomic and subatomic scales. It originates from quantum theory, a branch of physics that emerged in the early 20th century to explain phenomena observed on very small scales, where classical physics fails to provide accurate explanations. In the context of quantum theory, several key concepts are associated with the term quantum: Quantum mechanics: This is the branch of...
quantum sensing
Quantum sensing refers to a class of sensing technologies that leverage principles from quantum mechanics to enhance the precision and sensitivity of measurements. Traditional sensors operate based on classical physics, but quantum sensing exploits quantum properties, such as superposition and entanglement, to achieve improved performance in terms of accuracy, resolution, and sensitivity. Key concepts and characteristics of quantum sensing include: Superposition: Quantum sensors can...
quantum entanglement
Quantum entanglement is a phenomenon in quantum mechanics where two or more particles become correlated to such an extent that the state of one particle instantly influences the state of the other(s), regardless of the distance separating them. This means that the properties of each particle, such as position, momentum, spin, or polarization, are interdependent in a way that classical physics cannot explain. When particles become entangled, their individual quantum states become inseparable,...
photon
A quantum of electromagnetic energy of a single mode; i.e., a single wavelength, direction and polarization. As a unit of energy, each photon equals hn, h being Planck's constant and n, the frequency of the propagating electromagnetic wave. The momentum of the photon in the direction of propagation is hn/c, c being the speed of light.
quantum mechanics
The science of all complex elements of atomic and molecular spectra, and the interaction of radiation and matter.
Research & Technologyquantumquantum sensingentanglementquantum entanglementphotonphotonsoscillatorquantum mechanicsdielectric membranezero-point fluctuationsLIGOEuropemirrorsNiels BohrNiels Bohr InstituteUniversity of Copenhagen

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