Physicists have come up with a “quantum flute” that can make particles of light move together in a way that’s never been seen before. It is a discovery that could help improve future quantum computer designs.
University of Chicago’s Assoc. Prof. David Schuster and his colleagues study quantum bits. These are the quantum equivalent of a computer bit, only they make use of the bizarre properties of particles at the atomic and sub-atomic level to do things that are otherwise impossible.
Their latest experiment involved particles of light, known as photons, in the microwave spectrum.
Quantum Information Notes
Schuster’s lab designed a system consisting of a long chamber inside a block of metal, in order to trap photons at microwave frequencies. The cavity is made by drilling offset holes — just like holes in a flute.
“Just like in the musical instrument, you can send one or several wavelengths of photons across the whole thing, and each wavelength creates a ‘note’ that can be used to encode quantum information,”
Controlling the interactions of the “flute notes” can then be done by using a master quantum bit, a superconducting qubits electrical circuit.
Their oddest discovery, however, was the way the photons acted together.
The Tipping Point
Interaction between photons is hardly ever observed in nature, as they simply pass through each other. With exacting preparation, scientists can sometimes nudge two photons to react to each other’s presence.
“Here we do something even weirder. At first the photons don’t interact at all, but when the total energy in the system reaches a tipping point, all of a sudden, they’re all talking to each other,”
“Normally, most particle interactions are one-on-one — two particles bouncing or attracting each other. If you add a third, they’re usually still interacting sequentially with one or the other. But this system has them all interacting at the same time,”
Their tests only ran up to five “notes” together at one time, but the scientists could imagine running eventually hundreds or thousands of notes through a single qubit to control them. Building a quantum computer with 1,000 bits and controlling all of them through a single bit would be incredibly valuable, according to Schuster.
Srivatsan Chakram et al, Seamless High- Q Microwave Cavities for Multimode Circuit Quantum Electrodynamics, Physical Review Letters (2021). DOI: 10.1103/PhysRevLett.127.107701
Srivatsan Chakram et al, Multimode photon blockade, Nature Physics (2022). DOI: 10.1038/s41567-022-01630-y