An artist's impression of distributed qubits (the bright spots) linked to each other via photons (the light beams) (CREDIT: Mete Atature)

Laser-like photons could lead to 'quantum internet'

New research shows high-quality photons can be generated from solid-state chips bringing a “quantum internet” a step closer.

Researchers from the Cavendish Laboratory at Cambridge University have implemented a novel technique to generate single photons with tailored properties from solid-state devices that are identical in quality to lasers.

Single photons will form an integral part of distributed quantum networks, or a “quantum internet”, as flying units of quantum information called qubits as they carry information quickly and reliably across long distances and can take part in quantum logic operations provided all the photons taking part are identical.

But the quality of photons generated from solid-state qubits can be low due to decoherence mechanisms within the materials meaning each emitted photon is distinct from the others – a major roadblock to developing a quantum photonic network.

But in research published yesterday in the journal Nature Communications the researchers from Cambridge have outlined a solution to the problem.

"Our research has added the concepts of coherent photon shaping and generation to the toolbox of solid-state quantum photonics," said Dr Mete Atature from the Department of Physics, who led the research.

"We are now achieving a high-rate of single photons which are identical in quality to lasers with the further advantage of coherently programmable waveform; a significant paradigm shift to the conventional single photon generation via spontaneous decay."

As their photon source, the team built a semiconductor Schottky diode device containing individually addressable quantum dots, qubits made of semiconductor nanocrystals embedded in a chip that can be controlled electro-optically.

The transitions of quantum dots were used to generate single photons via resonance fluorescence – a technique demonstrated previously by the same team.

Under weak excitation, also known as the Heitler regime, the main contribution to photon generation is through elastic scattering and by operating in this way, photon decoherence can be avoided altogether.

The researchers were able to quantify how similar these photons are to lasers in terms of coherence and waveform and it turned out they were identical.

There are already protocols proposed for quantum computing and communication which rely on this photon generation scheme, and this work can be extended to other single photon sources as well, such as single molecules, colour centres in diamond and nanowires.

"We are at the dawn of quantum-enabled technologies, and quantum computing is one of many thrilling possibilities," added Dr Atature.

"Our results in particular suggest that multiple distant qubits in a distributed quantum network can share a highly coherent and programmable photonic interconnect that is liberated from the detrimental properties of the chips.

“Consequently, the ability to generate quantum entanglement and perform quantum teleportation between distant quantum-dot spin qubits with very high fidelity is now only a matter of time."

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