A laser pulse that sidesteps the inherent symmetry of light waves could manipulate quantum information, potentially bringing us closer to room temperature quantum computing.
While laser pulses can be used to manipulate the energy states of qubits, different ways of computing are possible if charge carriers used to encode quantum information could be moved around—including a room-temperature approach. Terahertz light, which sits between infrared and microwave radiation, oscillates fast enough to provide the speed, but the shape of the wave is also a problem. Namely, electromagnetic waves are obliged to produce oscillations that are both positive and negative, which sum to zero.
The positive cycle may move charge carriers, such as electrons. But then the negative cycle pulls the charges back to where they started. To reliably control the quantum information, an asymmetric light wave is needed.
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 researchers 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. (Phys.org)
The paper has been published in Light: Science & Applications.
