Photon qubits advance quantum computing without error correction techniques

This innovation addresses one of quantum computing's primary challenges: errors that escalate as computational demands grow. To mitigate this, researchers often employ the Variational Quantum Eigensolver (VQE), a hybrid algorithm that leverages both quantum and classical processing units for efficient computation. Despite its potential, VQE has been constrained by qubit limitations, with implementations capped at 2 qubits in photonic systems and 12 in superconducting systems, and plagued by scaling difficulties due to error rates.

The KIST team overcame these barriers by using qudits instead of qubits. Unlike qubits, which only represent 0 and 1 states, qudits allow for multiple states such as 0, 1, and 2, enabling more intricate quantum computations. In their study, the team implemented qudits using the orbital angular momentum state of single photons, manipulating photon phases through holographic imaging to expand dimensionality without relying on complex quantum gates. This method significantly reduced errors and simplified computations.

Their approach enabled them to perform high-dimensional quantum chemistry calculations. Using VQE, they estimated bond lengths for hydrogen molecules in four dimensions and lithium hydride (LiH) molecules in 16 dimensions - the first demonstration of 16-dimensional calculations in photonic systems. Unlike conventional methods, which require error mitigation to achieve chemical accuracy, the KIST team's approach achieved this precision without additional correction techniques.

These advancements suggest transformative applications in industries where molecular properties are critical. Potential uses include drug discovery, battery optimization, and even climate modeling, where high-dimensional quantum computations could yield groundbreaking insights.

"By securing qudit-based quantum computing technology that can achieve chemical accuracy with fewer resources, we expect it to be used in various practical fields, such as developing new drugs and improving battery performance," explained Dr. Hyang-Tag Lim of KIST.

Research Report:Qudit-based variational quantum eigensolver using photonic orbital angular momentum states