One of the most pursued challenges in electronics is the realisation of faster and more efficient transistors to compensate the overgrowing demand for higher computational speed and fast communication channels. Until the beginning of this century the clock speed of common microprocessors has more than doubled each year, reaching a limit, though, dictated by the problem of the constant increase in leakage currents, power consumption and heating. Optics, on the other hand, has already shown to overcome electronics for long distance communication and it is increasingly acquiring a leading role also in signal communications with in the CPU. However, one of the major challenge is to make photons interacting in an optical gate, something essential for the operation of transistor.
On the other hand, there is a novel technological revolution, which is the one of quantum information processing, i.e. how quantum physics allow a new type of processing of information. As an examples the Shor’s quantum algorithm could be capable of braking a cryptographic code by using a “quantum Fourier transform” that basically tries all the factorization simultaneously and solves the problem in a way that remains out of reach for a classical computer. There is therefore a huge incentive to build such a quantum computer, that would solve this and other classes of problems (database searching, linear equations solving, etc.) by manipulating “qubits” (quantum bits) and making them interfere in a quantum gate. However, despite the strong effort dedicated to this field the major problem to overcome is that it is difficult to bring together two basic requirements of this technology: maintaining quantum coherence and controlling the interactionbetween qubits. Photons, the elementary particles of light, have been extremely promising as carriers of quantum information (being very resilient against noise) however, even in this case, they lack of a fundamental property to make a quantum gate: the possibility to interact.
The main objective of ALADIN is, therefore, the study of a new generation of optical devices that could process signals similarly to present processors but without being affected by the high dissipation of purely electronic components. The ultimate extension of this goal is the realisation of devices that would work with only a single quantum of excitation. In other words, we propose to use a few photons to make operations that would either power a classical computer or could be used for quantum computation.
As fundamental propeller, is the very high admixture of light and matter that, if strong enough, would lead to a new quasiparticle called polariton. Such quasiparticles appear in semiconductors when a state of light (photons) and matter (electron-hole pairs, or excitons) couples strongly, combining antagonist properties of the two original particles, such as high coherence and strong interactions. As such, they appear ideal for both classical computation and quantum information processing, where these features are highly sought. Polaritons have been extremely successful in mesoscopic quantum physics by giving a new and applied dimension to fundamental concepts such as Bose-Einstein condensates (BEC) or superfluids, e.g., bringing them on-chip and up to room temperature. On the other hand they are developing quickly also for classical optical devices, with polariton transistors already demonstrated with the first AND and OR all-optical polariton gates working at low temperatures. All this, together with the observation of interactions at the single polariton level clearly promote polaritons, that–differently from simple photons–possess intrinsic interactions, as the best candidates, not only for classical but also for quantum computation.
However, there are still some gaps to be bridged and a few problems to be solved before such a technology could be truly mature. In terms of classical devices, all these results have been obtained with III-V semiconductors that could only work at temperatures below 15 K, which is prohibitive for technological applications. On the other hand, for quantum computation, while the problem of working at low temperature is not an immediate issue yet the amount of interactions of polaritons, in standard GaAs based semiconductors, is too low to give a significative throughput.
The principal direction of ALADIN is therefore a synergetic effort from different fields and expertise (material science, nano-processing, chemistry and photonics), most of which already present in the Institute of Nanotechnology, with the aim of studying new materials and optical systems for polaritonics that would increase the amount of interactions and bring the polariton devices to work at room temperature.
Back to New Research Initiatives