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Scientists open a new window into quantum physics with superconductivity in LEDs

March 18, 2014

Novel approach paves way for new quantum devices

TORONTO, ON — A team of Uni­ver­si­ty of Toron­to physi­cists led by Alex Hay­at has pro­posed a nov­el and effi­cient way to lever­age the strange quan­tum physics phe­nom­e­non known as entan­gle­ment. The approach would involve com­bin­ing light-emit­ting diodes (LEDs) with a super­con­duc­tor to gen­er­ate entan­gled pho­tons and could open up a rich spec­trum of new physics as well as devices for quan­tum tech­nolo­gies, includ­ing quan­tum com­put­ers and quan­tum com­mu­ni­ca­tion.

Entan­gle­ment occurs when par­ti­cles become cor­re­lat­ed in pairs to pre­dictably inter­act with each oth­er regard­less of how far apart they are. Mea­sure the prop­er­ties of one mem­ber of the entan­gled pair and you instant­ly know the prop­er­ties of the oth­er. It is one of the most per­plex­ing aspects of quan­tum mechan­ics, lead­ing Ein­stein to call it “spooky action at a dis­tance.”

“A usu­al light source such as an LED emits pho­tons ran­dom­ly with­out any cor­re­la­tions,” explains Hay­at, who is also a Glob­al Schol­ar at the Cana­di­an Insti­tute for Advanced Research. “We’ve proved that gen­er­at­ing entan­gle­ment between pho­tons emit­ted from an LED can be achieved by adding anoth­er pecu­liar phys­i­cal effect of super­con­duc­tiv­i­ty — a resis­tance-free elec­tri­cal cur­rent in cer­tain mate­ri­als at low tem­per­a­tures.”

This effect occurs when elec­trons are entan­gled in Coop­er pairs – a phe­nom­e­non in which when one elec­tron spins one way, the oth­er will spin in the oppo­site direc­tion. When a lay­er of such super­con­duct­ing mate­r­i­al is placed in close con­tact with a semi­con­duc­tor LED struc­ture, Coop­er pairs are inject­ed in to the LED, so that pairs of entan­gled elec­trons cre­ate entan­gled pairs of pho­tons. The effect, how­ev­er, turns out to work only in LEDs which use nanome­tre-thick active regions – quan­tum wells.

“Typ­i­cal­ly quan­tum prop­er­ties show up on very small scales – an elec­tron or an atom. Super­con­duc­tiv­i­ty allows quan­tum effects to show up on large scales – an elec­tri­cal com­po­nent or a whole cir­cuit. This quan­tum behav­iour can sig­nif­i­cant­ly enhance light emis­sion in gen­er­al, and entan­gled pho­ton emis­sion in par­tic­u­lar,” Hay­at said.

Oth­er U of T team mem­bers are physi­cists Hae-Young Kee, Ken­neth S. Burch and Aephraim M. Stein­berg. The research was pub­lished in Phys­i­cal Review B, an inter­na­tion­al jour­nal spe­cial­iz­ing in con­densed-mat­ter phe­nom­e­na and mate­ri­als physics on March 10.

Full arti­cle:


Alex Hay­at
Now at: Tech­nion, Israel Insti­tute of Tech­nol­o­gy
Tel: +972–4‑829‑4682

Kim Luke
Com­mu­ni­ca­tions, Fac­ul­ty of Arts & Sci­ence
Uni­ver­si­ty of Toron­to
Tel: 416–978-4352