The Faraon group and collaborators have developed an approach for quantum storage could help pave the way for the development of large-scale optical quantum networks.
The new system relies on nuclear spins—the angular momentum of an atom’s nucleus—oscillating collectively as a spin wave. This collective oscillation effectively chains up several atoms to store information.
Read the paper Ruskuc, Andrei and Wu, Chun-Ju and Rochman, Jake and Choi, Joonhee and Faraon, Andrei (2022) Nuclear spin-wave quantum register for a solid state qubit. Nature, 602 (7897). pp. 408-413 and the Caltech Media story: Chaining Atoms Together Yields Quantum Storage
Artist’s illustration depicts the quantum spin of an ytterbium ion with the surrounding yttrium orthovanadate crystal. The spin states of the atoms can be used as a processing unit (like transistors on a computer chip). By using the ytterbium to control four vanadium atoms simultaneously, the engineers were able to realize a 2-qubit processor, an important building block in the development of quantum computers and quantum networks. Credit: MAAYAN VISUALS
The work, which is described in a paper published on February 16 in the journal Nature, utilizes a quantum bit (or qubit) made from an ion of ytterbium (Yb), a rare earth element also used in lasers. The team, led by Andrei Faraon (BS ’04), professor of applied physics and electrical engineering, embedded the ion in a transparent crystal of yttrium orthovanadate (YVO4) and manipulated its quantum states via a combination of optical and microwave fields. The team then used the Yb qubit to control the nuclear spin states of multiple surrounding vanadium atoms in the crystal.
A new technique to utilize entangled nuclear spins as a quantum memory was inspired by methods used in nuclear magnetic resonance (NMR).
“To store quantum information in nuclear spins, we developed new techniques similar to those employed in NMR machines used in hospitals,” says Joonhee Choi, a postdoctoral fellow at Caltech and co-corresponding author of the paper. “The main challenge was to adapt existing techniques to work in the absence of a magnetic field.”
A unique feature of this system is the pre-determined placement of vanadium atoms around the ytterbium qubit as prescribed by the crystal lattice. Every qubit the team measured had an identical memory register, meaning it would store the same information.
“The ability to build a technology reproducibly and reliably is key to its success,” says graduate student Andrei Ruskuc, first author of the paper. “In the scientific context, this let us gain unprecedented insight into microscopic interactions between ytterbium qubits and the vanadium atoms in their environment.”
