New quantum device uses crystal layers to generate entangled photons

Researchers around the world have chased the promise of quantum entanglement in a device for years.

The concept, often called spooky action at a distance, happens when two particles become linked so intensely that changing the state of one instantly changes the state of the other – even if they sit thousands of miles apart. 

Scientists first discussed the idea as early as 1935, and it sparked passionate debate in the physics community.

Biggest issue for quantum devices

Classical research methods showed that generating entangled photons often required large crystals and hefty amounts of energy. Smaller, more efficient systems long stood as a kind of holy grail for quantum device engineers. 

Many believed a lighter, more compact approach might offer a real shot at quantum-based telecommunications and computing.

Yet design challenges kept mounting, and experts struggled to shrink the necessary components enough to fit on a chip.

P. James Schuck, associate professor of mechanical engineering at Columbia Engineering, helped guide a fresh effort to overcome these hurdles.

He and his collaborators created a new entangled photon-pair source that is more efficient than previous models while requiring far less space. 

Their paper, published in Nature Photonics, showcases a method that reduces energy use while squeezing everything into a device that is just 3.4 micrometers thick.

A closer look at van der Waals materials

The breakthrough quantum device hinges on a stack of six ultra-thin crystal pieces made from molybdenum disulfide. Researchers rotated each piece 180 degrees relative to the layer above and below. 

They employed an approach called quasi-phase-matching, which alters the properties of light in a way that allows for the creation of paired photons. 

Scientists have used quasi-phase-matching for years, but turning to van der Waals semiconductors for this process was a bold move because these materials can pack impressive optical capabilities in an extremely tight space.

Quashing interference in tiny layers

Periodically flipping each crystal slice solves a classic interference problem.

When light waves travel in uniform directions within certain materials, they start canceling one another, which limits performance.

This periodic flipping trick keeps the waves in check and preserves the desired signals. 

“This work represents the embodiment of the long-sought goal of bridging macroscopic and microscopic nonlinear and quantum optics,” said Schuck.

Quantum entanglement device

Entangled-photon pairs form a fundamental building block of many quantum systems.

Engineers count on them for encryption, sensing applications, and the creation of qubits for quantum computing. Smaller generators that use less power could mean more compact setups. 

“These innovations will have an immediate impact in diverse areas including satellite-based distribution and mobile phone quantum communication,” said Schuck. He and his team anticipate wide-ranging possibilities.

Simple devices that generate entangled photons at telecom wavelengths stand to revolutionize encryption, teleconferencing, and large-scale data transfer. Quantum key distribution could become less expensive and more secure.

Some sensor arrays might gain speed and sensitivity if entangled pairs arrive faster and consume less battery power.

The team’s research shows that a van der Waals system can handle these demands without the size or energy constraints of older setups.

One step toward on-chip integration

Bringing quantum light sources onto a silicon chip like Google’s Quantum chip, Willow, could change the face of computing and telecommunications. This new device hints at the potential for integrated circuits that handle quantum signals. 

“It provides the foundation for scalable, highly efficient on-chip integrable devices such as tunable microscopic entangled-photon-pair generators,” stated Schuck at the end of a recent announcement.

Making everything smaller and more efficient sets the stage for eventual commercial designs, including portable quantum devices.

Future research

There is a growing drive to develop on-chip quantum elements that do more than just produce photon pairs. In the future, integrated setups might include photon detectors, modulators, and memory elements. 

At that point, systems could become easier to mass-produce. Different industries might adapt them for network security, advanced diagnostics, or near-instant long-distance communication.

With this step, researchers encourage the idea that quantum architectures can finally go mainstream.

Simpler, portable quantum chip devices

The race is on to convert big, clunky research tools into simple, reliable instruments.

In time, groups outside specialized labs may deploy quantum sensors for medical imaging, environmental monitoring, and more. 

The engineering behind these stacked crystals is still new, but early results are setting optimistic expectations. By sidestepping older size and energy limits, the team has charted a path that many others might soon follow.

The study is published in Nature Photonics.

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