Scientists at Paderborn University have made a further step forward in the field of quantum research: for the first time ever, they have demonstrated a cryogenic circuit (i.e. one that operates in extremely cold conditions) that allows light quanta—also known as photons—to be controlled more quickly than ever before.

Specifically, these scientists have discovered a way of using circuits to actively manipulate light pulses made up of individual photons. This milestone could substantially contribute to developing modern technologies in quantum information science, communication and simulation. The results have now been published in the journal Optica.

Photons, the smallest units of light, are vital for processing quantum information. This often requires measuring a photon’s state in real time and using this information to actively control the luminous flux—a method known as a “feedforward operation.”

However, thus far this has butted up against technical limitations: light was measured, processed and controlled at a delay, limiting its use for complex applications. With their new method, these scientists have managed to significantly reduce the delay—to less than a quarter of a billionth of a second.

“We have managed to actively interconnect light pulses with detectors, adapted electronics and optical circuits at cryogenic temperatures. This enabled us to manipulate individual photons significantly more quickly than other research groups. The ability allows us to create new active circuits for quantum optics that can be used for a variety of applications,” explains Dr. Frederik Thiele, who is spearheading the project with Niklas Lamberty, both members of the “Mesoscopic Quantum Optics” research group at Paderborn’s Department of Physics.

The researchers used state-of-the-art technologies such as superconducting detectors for this development. These devices measure individual light quanta with extremely high precision.

The electronics were deployed in a cryogenic environment: the amplifier and modulators were operated at temperatures of around -270 degrees Celsius in order to process signals without any significant delay. Integrated modulators are optical components that control the light based on measurement data—virtually loss-free and at high speeds.

The process is based on measuring light pairs, or “correlated photons.” Based on the number of particles measured, the electronic circuit decides in a fraction of a second whether the light should be forwarded or blocked. What makes the integrated design special is that physical losses and delays can be reduced to a minimum.

As well as a fast response, the circuit also produces less heat, which is vital when working in cryostats (extreme cooling systems) in very small spaces.

“Our demonstration shows that we can use superconducting and semiconducting technology to achieve a new level of photonic quantum control. This opens up opportunities for fast and complex quantum circuits, which could be vitally important for quantum information science and communication,” Thiele summarizes.