Single Photon Switch Can Speed Computation Up to 1,000 times

An international research team led by Skoltech and IBM has created an extremely energy-efficient optical switch that could replace electronic transistors in a new generation of computers manipulating photons rather than electrons. In addition to direct power saving, the switch requires no cooling and is really fast: At 1 trillion operations per second, it is between 100 and 1,000 times faster than today’s top-notch commercial transistors.

It only takes a few photons to switch per the author of the study, Dr. Anton Zasedatelev. They achieved switching with just one photon at room temperature. There will be a lot of work to scale the proof-of-principle demonstration into an all-optical co-processor.

Nature – Single-photon nonlinearity at room temperature

Most modern electrical transistors take tens of times more energy to switch, and the ones that use single electrons to achieve comparable efficiencies are way slower.

Competing power-saving electronic transistors need bulky cooling equipment, which in turn consumes power and factors into the operating costs. The new switch conveniently works at room temperature and therefore circumvents all these problems.

In addition to its primary transistor-like function, the switch could act as a component that links devices by shuttling data between them in the form of optical signals. It can also serve as an amplifier, boosting the intensity of an incoming laser beam by a factor of up to 23,000.

How it works

The device relies on two lasers to set its state to “0” or “1” and to switch between them. A very weak control laser beam is used to turn another, brighter laser beam on or off. It only takes a few photons in the control beam, hence the device’s high efficiency.

The switching occurs inside a microcavity — a 35-nanometer thin organic semiconducting polymer sandwiched between highly reflective inorganic structures. The microcavity is built in such a way as to keep incoming light trapped inside for as long as possible to favor its coupling with the cavity’s material.

This light-matter coupling forms the basis of the new device. When photons couple strongly to bound electron-hole pairs — aka excitons — in the cavity’s material, this gives rise to short-lived entities called exciton-polaritons, which are a kind of quasiparticles at the heart of the switch’s operation.

When the pump laser — the brighter one of the two — shines on the switch, this creates thousands of identical quasiparticles in the same location, forming so-called Bose-Einstein condensate, which encodes the “0” and “1” logic states of the device.

To switch between the two levels of the device, the team used a control laser pulse seeding the condensate shortly before the arrival of the pump laser pulse. As a result, it stimulates energy conversion from the pump laser, boosting the amount of quasiparticles at the condensate. The high amount of particles in there corresponds to the “1” state of the device.

The researchers used several tweaks to ensure low power consumption:
1. efficient switching was aided by the vibrations of the semiconducting polymer’s molecules. The trick was to match the energy gap between the pumped states and the condensate state to the energy of one particular molecular vibration in the polymer.
2. the team managed to find the optimal wavelength to tune their laser to and implemented a new measurement scheme enabling single-shot condensate detection.
3. the control laser seeding the condensate and its detection scheme were matched in a way that suppressed the noise from the device’s “background” emission. These measures maximized the signal-to-noise level of the device and prevented an excess of energy from being absorbed by the microcavity, which would only serve to heat it up through molecular vibrations.

“There’s still some work ahead of us to lower the overall power consumption of our device, which is currently dominated by the pump laser that keeps the switch on. A route toward that goal could be perovskite supercrystal materials like those we’re exploring with collaborators. They have proven excellent candidates given their strong light-matter coupling which in turn leads to a powerful collective quantum response in the form of superfluorescence,” the team comments.

This is one of many components needed for all optical computers that would manipulate photons instead of electrons, resulting in vastly superior performance and lower power consumption.

The recent progress in nanotechnology and single-molecule spectroscopy paves the way for emergent cost-effective organic quantum optical technologies with potential applications in useful devices operating at ambient conditions. We harness a π-conjugated ladder-type polymer strongly coupled to a microcavity forming hybrid light–matter states, so-called exciton-polaritons, to create exciton-polariton condensates with quantum fluid properties. Obeying Bose statistics, exciton-polaritons exhibit an extreme nonlinearity when undergoing bosonic stimulation6, which we have managed to trigger at the single-photon level, thereby providing an efficient way for all-optical ultrafast control over the macroscopic condensate wavefunction. Here, we utilize stable excitons dressed with high-energy molecular vibrations, allowing for single-photon nonlinear operation at ambient conditions. This opens new horizons for practical implementations like sub-picosecond switching, amplification and all-optical logic at the fundamental quantum limit.

Written by Brian Wang,

2 thoughts on “Single Photon Switch Can Speed Computation Up to 1,000 times”

  1. Brian, I think you got the picture for this article mixed up. This article is about CPU technology, but the graphic is about solar sails.

  2. Anyone interested in beyond Moore's law possibilities should seek out Ralph Merkle's highly theoretical work on molecular mechanical computing. Very interesting stuff.

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