Twisty photons could enhance next-generation quantum communication

A quantum emitter capable of emitting single photons integrated with a gear-shaped resonator. By fine-tuning the arrangement of the emitter and resonator in the shape of a gear, it is possible to exploit the interaction between the spin of the photon and its orbital angular momentum to create single “twisting” photons on demand. Credit: Stevens Institute of Technology

Quantum computers and communication devices work by encoding information into individual or entangled photons, allowing data to be transmitted and quantistically manipulated securely, exponentially faster than is possible with conventional electronics. Now, quantum researchers at the Stevens Institute of Technology have demonstrated a method for encoding much more information into a single photon, opening the door to even faster and more powerful quantum communication tools.

Typically, quantum communication systems “write” information about the spin angular momentum of a photon. In this case, the photons make a right or left circular rotation or form a quantum superposition of the two known as a two-dimensional qubit.

It is also possible to encode information about a photon’s orbital angular momentum, the corkscrew path that light follows as it twists and twists forward, with each photon rotating around the center of the beam. When spin and angular momentum fit together, it forms a high-dimensional qudit, which allows any theoretically infinite range of values ​​to be encoded and propagated from a single photon.

Qubits and qudits, also known as flying qubits and flying qudits, are used to propagate information stored in photons from one point to another. The main difference is that qudits can carry much more information over the same distance than qubits, providing the foundation for the next generation quantum communication turbocharger.

In a cover story in the August 2022 issue of OpticsResearchers led by Stefan Strauf, head of Stevens’ NanoPhotonics Lab, show that they can create and control single flying qudits, or “twisting” photons, on demand, a breakthrough that could greatly expand the capabilities of quantum communication tools.

“Normally spin angular momentum and orbital angular momentum are independent properties of a photon. Our device is the first to demonstrate simultaneous control of both properties through controlled coupling between the two,” explained Yichen Ma, one graduate student at Strauf’s NanoPhotonics Lab, who conducted the research in collaboration with Liang Feng at the University of Pennsylvania and Jim Hone at Columbia University.

“What makes this a big deal is that we have shown that we can do this with single photons rather than classic light beams, which is the basic requirement for any type of quantum communication application,” said Ma.

Encoding information into orbital angular momentum radically increases the information that can be transmitted, explained Ma. Taking advantage of “winding” photons could increase the bandwidth of quantum communication tools, allowing them to transmit data much faster.

To create twisted photons, Strauf’s team used an atom-thick film of tungsten diselenide, a new upcoming semiconductor material, to create a quantum emitter capable of emitting single photons.

Next, they coupled the quantum emitter into an internally reflective donut-shaped space called a ring resonator. By fine-tuning the arrangement of the emitter and resonator in the shape of a gear, it is possible to exploit the interaction between the spin of the photon and its orbital angular momentum to create single “twisting” photons on demand.

The key to enabling this spin-momentum locking feature lies in the gear-shaped configuration of the ring resonator, which, when carefully engineered into the design, creates the twisty vortex light beam that the device fires at lightning speed.

By integrating these capabilities into a single microchip just 20 microns in diameter, about a quarter the width of a human hair, the team created a twisting photon emitter that can interact with other standardized components as part of a quantum communication system.

Some key challenges remain. Although the team’s technology can control the direction in which a photon moves in a spiral, clockwise or counterclockwise, more work is needed to control the exact number of modes of the orbital angular momentum. This is the critical capacity that will allow to “write” and subsequently extract from a single photon a theoretically infinite range of different values. The latest experiments in Strauf’s nanophotonics lab show promising results that this problem can be overcome soon, according to Ma.

Further work is also needed to create a device capable of creating convoluted photons with strictly coherent quantum properties, i.e. indistinguishable photons, a fundamental requirement for enabling the quantum internet. Such challenges affect everyone working in quantum photonics and may require new breakthroughs in materials science to be solved, Ma said.

“We have a lot of challenges ahead of us,” he added. “But we have shown the potential to create quantum light sources that are more versatile than anything previously possible.”

Tailor-made single photons: optical photon control as a key to new technologies

More information:
Yichen Ma et al, Blocking the spin-on-chip orbit of quantum emitters in 2D materials by chiral emission, Optics (2022). DOI: 10.1364 / OPTICA.463481

Provided by Stevens Institute of Technology

Citation: “Twisty” photons could enhance next-generation quantum communication (2022, September 22) recovered on September 23, 2022 from gen-quantum. html

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