Technion News: Opens a New Path for Quantum Data Transfer
The Technion's Nanophotonic Advance Doubles Quantum Secret Velocity
Technion News
A team of Technion-Israel Institute of Technology physicists and engineers has advanced quantum communication by creating and managing “high-dimensional” quantum states on a nanophotonic chip. By using metals' nanoscale nonlinear optical properties, the researchers could nearly treble quantum security protocols' data transmission rates.
Amit Kam, Liat Nemirovsky-Levy, and Distinguished Professor Mordechai Segev conducted the study. It addresses the size and complexity of devices needed to process complex quantum information, a major barrier to a quantum internet.
Beyond the Qubit: Qudit Power
“Qubit,” the quantum counterpart of a computer bit, has been the gold standard in quantum information for decades. However, qubits can only be 0 or 1. However, Technion researchers focused on qudits, quantum states with more than two layers. Quudits encode and process more data per mode than qubits. These multi-level states improve entanglement use in quantum systems, making them more compact and secure for teleportation and distributed computation.
Creating these states formerly required vast lab settings with elaborate mirror and laser arrays, but the new Technion technology fits the entire process into a nanophotonic platform suitable with on-chip technologies.
Using Nanoscale Nonlinearity
Nonlinear nanophotonics—the study of how light changes materials—led to the finding. The team exploited gold's third-order nonlinearity.
Once connected into the equipment, single photons become Surface Plasmon Polaritons (SPPs), which are light waves attached to a metal surface. SPPs' Total Angular Momentum (TAM) is a “good quantum number” for sub-wavelength information encoding.
The team modified this data with a powerful classical “pump” beam. The pump beam interacts with the SPP to “dress” the quantum state through four-wave mixing, which projects near-field data onto far-field OAM and SAM states.
Simply changing the pump beam's polarization from circular to linear allows the researchers to “at will” govern the semiconductor's high-dimensional states.
A New Quantum Security Standard
The researchers proposed a Quantum Key Distribution (QKD) protocol to demonstrate their invention's utility. Alice and Bob can exchange statistically impossible-to-crack secret encryption keys using QKD.
BB84 employs two-level qudits, but the Technion team uses four. Encoding the numerals 0, 1, 2, and 3 into the photons' SAM and OAM yields a double key rate compared to conventional methods. The scientists say their technology “generalizes the BB84 protocol to higher dimensions,” and their nanophotonic device's tight light confinement increases entangled photon generation.
Strong, Scalable Design
Outcoupling quantum information from the chip into free space for measurement is a major difficulty in quantum optics. Technion uses a gold-silica-silicon stack to improve interaction strength. Gold provides the necessary plasmonic localization while restricting light to silicon.
Based on realistic values, 118 photon counts per second are estimated. Modern single-photon detectors can detect this, indicating the technology is suitable for testing and development.
Future of On-Chip Quantum Computing
This work affects more than encrypted messaging. The platform's tight integration with on-chip photonic technology enables scalable distributed quantum networks and quantum computing.
Combining nanophotonics and nonlinear optics provides a “potential route for studying the interaction between nanophotonic field structure and quantum state control” for the researchers. As they shrink and become more environmental-resistant, these devices may provide the basis for a new generation of useful, compact quantum communication devices.
The team believes combining these platforms into on-chip technologies will enable “significant step toward realizing scalable quantum computing and communication systems” in the future.
