Research advances quantum computing that harnesses speed of light

Purdue University engineers have made strides in developing quantum photonic integrated circuits that could potentially harness the speed of light for faster and more energy-efficient quantum computing. Qubits, the quantum version of classical bits, can exist in both zero and one states simultaneously, vastly expanding the information that can be processed. Unlike bits, which can only be either zero or one, qubits represent both states at once through superposition, a phenomenon that greatly enhances computational power.

Photons, the smallest particles of light, offer several advantages over other quantum particles for qubit construction. They enable qubits to move through circuit gates at the speed of light, reducing data transfer delays and improving algorithm performance. Additionally, photons are less susceptible to disturbances such as heat, allowing them to maintain stability at room temperature, unlike other qubits that require cryogenic temperatures and consume more energy.

However, a major challenge in scaling up quantum photonic integrated circuits lies in creating single-photon sources and controlling photons using switches. A single photon serves as the building block for quantum photonics, but generating it consistently at room temperature and in a controlled manner has been difficult. In 2021, Vladimir Shalaev and Alexandra Boltasseva from Purdue's Elmore Family School of Electrical and Computer Engineering discovered a way to emit single photons using silicon nitride, a material commonly used in quantum photonic platforms.

To address the issue of uncontrolled photon emission, the researchers developed a method to emit exactly one photon at room temperature from multiple locations on a silicon nitride platform every time a laser beam passes through it. This breakthrough, published in Science Advances, involved creating atomic defects within the platform that limit light emission to a single photon at a time.

By embedding these defects in nanosized pillars on the silicon nitride platform, the researchers can control the placement and number of defects, enabling uniform manufacturing for quantum photonic integrated circuits.

Another challenge in building quantum photonic integrated circuits is the limited interaction between single photons, which makes them hard to control using switches. In conventional computers, transistors toggle bits between zero and one states for information processing. Similarly, switches in quantum photonic integrated circuits would enable photons to act as qubits.

In a Nature Nanotechnology paper, Shalaev and Boltasseva demonstrated a switch capable of operating on the level of single photons. This switch utilizes optical nonlinearity, a mechanism that allows a control light beam to interact with a probe beam, effectively switching the beam on and off based on the presence of a single photon.