Quantum entanglement at ambient conditions in a macroscopic solid-state spin ensemble
Entanglement is one of nature's most elusive phenomena. Producing entanglement between particles requires that they start out in a highly ordered state, which is disfavored by thermodynamics, the process that governs the interactions between heat and other forms of energy. This poses a particularly formidable challenge when trying to realize entanglement at the macroscopic scale, among huge numbers of particles.
“The macroscopic world that we are used to seems very tidy, but it is completely disordered at the atomic scale. The laws of thermodynamics generally prevent us from observing quantum phenomena in macroscopic objects,” said Paul Klimov, a graduate student in the University of Chicago’s Institute for Molecular Engineering and lead author of new research on quantum entanglement. The institute is a partnership between UChicago and Argonne National Laboratory.
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 (1000 times larger than that of a typical refrigerator magnet) or using chemical reactions. In the Nov. 20 issue of
Science Advances, Klimov and other researchers in David Awschalom's group at the Institute for Molecular Engineering have demonstrated that
macroscopic entanglement can be generated at room temperature and in a small magnetic field.
The researchers used infrared laser light to preferentially align the magnetic states of thousands of electrons and nuclei and then electromagnetic pulses, similar to those used for conventional magnetic resonance imaging (MRI), 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) of the semiconductor SiC to become entangled.
“We know that the spin states of atomic nuclei associated with semiconductor defects have excellent quantum properties at room temperature,” said Awschalom, Liew Family Professor in Molecular Engineering and a senior scientist at Argonne National Laboratory. “They are coherent, long-lived and controllable with photonics and electronics. Given these quantum ‘pieces,’ creating entangled quantum states seemed like an attainable goal.”