Quantum entanglement achieved at room temperature in macroscopic semiconductor wafers

November 23, 2015

Paul Klimov, a graduate student in the University of Chicago’s Institute for Molecular Engineering, adjusts the intensity of a laser beam during an experiment. (credit: Awschalom Group/University of Chicago)

Researchers in Prof. David Awschalom’s group at the Institute for Molecular Engineering have demonstrated macroscopic entanglement at room temperature and in a small (33 millitesla) magnetic field.

Previously, scientists have overcome the thermodynamic barrier and achieved macroscopic entanglement in solids and liquids by going to ultra-low temperatures (-270 degrees Celsius) and applying huge magnetic fields (1,000 times larger than that of a typical refrigerator magnet) or using chemical reactions.

In an open-access paper published in the Nov. 20 issue of Science Advances, the researchers explain that they used infrared laser light to order (preferentially align) the magnetic states of thousands of electrons and nuclei and then used electromagnetic pulses to entangle them. This procedure caused pairs of electrons and nuclei in a macroscopic 40 micrometer-cubed volume (the volume of a red blood cell) in a silicon carbide (SiC, also known as carborundum) semiconductor wafer to become entangled.

“The ability to produce robust entangled states in an electronic-grade semiconductor at ambient conditions has important implications on future quantum devices,” Awschalom said. In the short term, the research could enable quantum sensors that use entanglement as a resource for beating the sensitivity limit of traditional (non-quantum) sensors and for biological sensing inside a living organism, using entanglement-enhanced magnetic resonance imaging probes, according to the researchers.

They said that it might even be possible in the long term to go from entangled states on the same SiC chip to entangled states across distant SiC chips via macroscopic quantum states, as opposed to single quantum states (in single atoms). Such long-distance entangled states have been proposed for synchronizing global positioning satellites and for communicating information secured from eavesdroppers.

The institute is a partnership of the University of Chicago and and Argonne National Laboratory.

Abstract of Quantum entanglement at ambient conditions in a macroscopic solid-state spin ensemble

Entanglement is a key resource for quantum computers, quantum-communication networks, and high-precision sensors. Macroscopic spin ensembles have been historically important in the development of quantum algorithms for these prospective technologies and remain strong candidates for implementing them today. This strength derives from their long-lived quantum coherence, strong signal, and ability to couple collectively to external degrees of freedom. Nonetheless, preparing ensembles of genuinely entangled spin states has required high magnetic fields and cryogenic temperatures or photochemical reactions. We demonstrate that entanglement can be realized in solid-state spin ensembles at ambient conditions. We use hybrid registers comprising of electron-nuclear spin pairs that are localized at color-center defects in a commercial SiC wafer. We optically initialize 103 identical registers in a 40-μm3 volume (with Embedded Image fidelity) and deterministically prepare them into the maximally entangled Bell states (with 0.88 ± 0.07 fidelity). To verify entanglement, we develop a register-specific quantum-state tomography protocol. The entanglement of a macroscopic solid-state spin ensemble at ambient conditions represents an important step toward practical quantum technology.