Emulering af umulige unipolære laserimpulser baner vejen for behandling af kvanteinformation

En laserimpuls, der omgår lysbølgernes iboende symmetri, kunne manipulere kvanteinformation og potentielt bringe os tættere på rumtemperatur kvanteberegning.

Undersøgelsen, ledet af forskere ved University of Regensburg og University of Michigan, kunne også fremskynde konventionel databehandling.

Kvantecomputere har potentialet til at fremskynde løsninger på problemer, der skal udforske mange variabler på samme tid, herunder lægemiddelopdagelse, vejrudsigelse og kryptering til cybersikkerhed. Konventionelle computerbits koder enten 1 eller 0, men kvantebits eller qubits kan kode begge på samme tid. Dette gør det i det væsentlige muligt for kvantecomputere at arbejde gennem flere scenarier samtidigt, i stedet for at udforske dem efter hinanden. Disse blandede tilstande varer dog ikke længe, ​​så informationsbehandlingen skal være hurtigere, end elektroniske kredsløb kan mønstre.

Mens laserimpulser kan bruges til at manipulere energitilstande af qubits, er forskellige måder at beregne på, mulige, hvis ladningsbærere, der bruges til at kode kvanteinformation, kunne flyttes rundt - inklusive en stuetemperaturtilgang. Terahertz-lys, som sidder mellem infrarød og mikrobølgestråling, svinger hurtigt nok til at give hastigheden, men formen på bølgen er også et problem. Elektromagnetiske bølger er nemlig forpligtet til at producere svingninger, der er både positive og negative, som summerer til nul.

Den positive cyklus kan flytte ladningsbærere, såsom elektroner. Men så trækker den negative cyklus ladningerne tilbage til hvor de startede. For pålideligt at kontrollere kvanteinformationen er en asymmetrisk lysbølge nødvendig.

"Det optimale ville være en fuldstændig retningsbestemt, unipolær 'bølge', så der ville kun være den centrale top, ingen svingninger. Det ville være drømmen. Men virkeligheden er, at lysfelter, der forplanter sig, skal oscillere, så vi forsøger at lave the oscillations as small as we can," said Mackillo Kira, U-M professor of electrical engineering and computer science and leader of the theory aspects of the study in Light:Science &Applications .

Since waves that are only positive or only negative are physically impossible, the international team came up with a way to do the next best thing. They created an effectively unipolar wave with a very sharp, high-amplitude positive peak flanked by two long, low-amplitude negative peaks. This makes the positive peak forceful enough to move charge carriers while the negative peaks are too small to have much effect.

They did this by carefully engineering nanosheets of a gallium arsenide semiconductor to design the terahertz emission through the motion of electrons and holes, which are essentially the spaces left behind when electrons move in semiconductors. The nanosheets, each about as thick as one thousandth of a hair, were made in the lab of Dominique Bougeard, a professor of physics at the University of Regensburg in Germany.

Then, the group of Rupert Huber, also a professor of physics at the University of Regensburg, stacked the semiconductor nanosheets in front of a laser. When the near-infrared pulse hit the nanosheet, it generated electrons. Due to the design of the nanosheets, the electrons welcomed separation from the holes, so they shot forward. Then, the pull from the holes drew the electrons back. As the electrons rejoined the holes, they released the energy they'd picked up from the laser pulse as a strong positive terahertz half-cycle preceded and followed by a weak, long negative half-cycle.

"The resulting terahertz emission is stunningly unipolar, with the single positive half-cycle peaking about four times higher than the two negative ones," Huber said. "We have been working for many years on light pulses with fewer and fewer oscillation cycles. The possibility of generating terahertz pulses so short that they effectively comprise less than a single half-oscillation cycle was beyond our bold dreams."

Next, the team intends to use these pulses to manipulate electrons in room temperature quantum materials, exploring mechanisms for quantum information processing. The pulses could also be used for ultrafast processing of conventional information.

"Now that we know the key factor of unipolar pulses, we may be able to shape terahertz pulses to be even more asymmetric and tailored for controlling semiconductor qubits," said Qiannan Wen, a Ph.D. student in applied physics at U-M and a co-first-author of the study, along with Christian Meineke and Michael Prager, Ph.D. students in physics at the University of Regensburg. + Udforsk yderligere

Light could make semiconductor computers a million times faster or even go quantum