Enhanced wavelength conversion for quantum information transfer

Advancements in quantum information technology are paving the way for more efficient data transfer. A key challenge has been ensuring that qubits, the units of quantum information, can be transferred between different wavelengths without losing their essential properties, such as coherence and entanglement.

Now, researchers from Shanghai Jiao Tong University (SJTU) have developed a method for broadband frequency conversion, marking a step forward for future quantum networks. The SJTU team focused on a technique using X-cut thin film lithium niobate (TFLN), a material known for its nonlinear optical properties. The researchers achieved second-harmonic generation — an important process for converting light from one wavelength to another — with a bandwidth of up to 13 nanometres. This was accomplished through a process called mode hybridisation, which allows for precise control over the frequency conversion in a micro-racetrack resonator.

Corresponding author Yuping Chen said an efficient second-order nonlinear process with widely tuneable pump bandwidth has been a long-pursued goal, due to the extensive applications in wavelength division multiplexing networks, ultrashort pulse nonlinearity, quantum key distribution and broadband single-photon source generation.

“Thanks to the great progress in fabrication technology on the TFLN platform, this work will pave the way to chip-scale nonlinear frequency conversion between the ultrashort optical pulses and even the quantum states,” Chen said.

The research findings could have wide-ranging implications for integrated photonic systems. By enabling on-chip tuneable frequency conversion, the new method opens the door to enhanced quantum light sources, larger capacity multiplexing and more effective multichannel optical information processing.

Top image caption: Dispersion-designed structural geometry enables group-velocity mismatch of interacting lights to be smoothed to zero, for wide-range frequency conversion. Image credit: T. Yuan, J. Wu, SPIE.