Researchers the Department of Energy's Oak Ridge National Laboratory have demonstrated a new level of control they have gained over photons encoded with quantum information.
Joseph Lukens, Brian Williams, Nicholas Peters and Pavel Lougovski, scientists and researchers in ORNL's Quantum Information Science Group, performed separate and independent operations simultaneously on two qubits encoded with photons of different frequencies. Qubits are the smallest units of quantum information.
Quantum scientists, working with frequency-encoded qubits, have managed to perform a single operation on two qubits in parallel, but quantum computing has achieved something else.
"To achieve universal quantum computing, we need to be able to perform different operations on different qubits simultaneously, and that's what we did here," Lougovski said.
According to Lougovski, the team's experimental system – two photons contained in a single strand of fiber optic cable – is "the smallest quantum computer you can imagine. This research marks the first demonstration of our frequency-based approach to global quantum computing."
“A lot of researchers are talking about processing quantum information with photons, even using frequencies,” Lukens said. “But no one had thought about sending multiple photons through the same optical fiber, into the same space, and performing different operations on them.”
The team's quantum frequency processor allowed them to manipulate the frequency of photons to induce superposition, a state that enables quantum operations and computational capability.
Unlike data bits encoded for classical computers, superposed qubits encoded at photon frequencies have a value of 0 and 1 rather than 0 or 1. This capability allows quantum computers to simultaneously perform operations on larger data sets than today's supercomputers.
Using their processor, the researchers demonstrated 97% visibility of the interference – a measure of how similar two photons are – compared to the 70% visibility rate of a similar study. Their result showed that the photons' quantum states were nearly identical.
The researchers also applied a statistical method related to machine learning to demonstrate that the tasks were performed with very high fidelity and in a completely controlled manner.
