Thewalt Lab at SFU
Impurities as qubits in semiconductors Much of our recent work is based on our earlier discovery that many optical transitions are much sharper in enriched 28Si than they are in natural silicon. In particular, we have shown that this increased resolution allows us to observe the hyperfine splitting resulting from the coupling of the donor electron and nuclear spins in the donor bound exciton transitions. We can use these transitions to optically measure the donor electron and nuclear spins, and to hyperpolarize them. This has many applications for research in semiconductor-based quantum information, since the donor electron and nuclear spins are prime qubit candidates. It has already lead to the measurement of record quantum coherence times for a solid-state system. Future directions will expand beyond the prototypical donor in silicon, phosphorus, to study deeper donors such as bismuth, which has a much larger hyperfine interaction, and a large I=9/2 nuclear spin. Other Research
Aliasing and the Heisenberg uncertainty principle.
The Heisenberg uncertainty principle says that if you have a particle in some state and observe either its momentum or its position then the products of the standard deviations of distributions of the outcomes satisfy this identity: Here's another way of thinking about that kind of picture (assuming some units I haven't specified): The idea is that the question mark represents digits we don't know well. But this picture is highly misleading. In other words, it's compatible with the uncertainty principle that we could know the digits beyond the decimal point to as much accuracy as we like as long as we don't know the digits before the point. But being compatible with Heisenberg uncertainty isn't enough for something to be realisable as a physical state. Sampling audio and graphics Maybe surprisingly, the worlds of audio and graphics can help us answer this question. The red curve here is just to show what the original waveform looked like. The connection to physics What this means
Record du monde d'intrication quantique : 14 qubits !
Un groupe de physiciens de l'Université d'Innsbruck vient de battre un nouveau record dans le domaine de l'information quantique en réussissant à intriquer 14 atomes de calcium dans un piège à ions. Cette performance est un pas de plus en direction d'un mythique ordinateur quantique capable de battre les superordinateurs classiques. Ce sont Albert Einstein et surtout Erwin Schrödinger qui ont les premiers compris que les équations de la mécanique quantique contenaient le mystérieux phénomène de l'intrication. Il se manifeste dans le cas du paradoxe EPR et dans celui du fameux chat de Schrödinger. Le premier a été observé par le physicien Alain Aspect et la résolution au moins partielle du second a été apportée théoriquement par Wojciech Zurek et observée expérimentalement par Serge Haroche. L'intrication quantique pourrait permettre de fabriquer des ordinateurs capables de résoudre plus rapidement certains problèmes qui demandent aujourd'hui encore l'aide de supercalculateurs.
D-Wave’s quantum optimizer might be quantum after all
Quantum optimizer manufacturer D-Wave Systems has been gaining a lot of traction recently. They've sold systems to Lockheed Martin and Google, and started producing results showing that their system can solve problems that are getting closer to having real-life applications. All in all, they have come a long way since the first hype-filled announcement. Over time, my skepticism has waxed and waned. Although I didn't really trust their demonstrations, D-Wave's papers, which usually made more limited claims, seemed pretty solid. Once again in English, please Annealing is a process where you carefully and slowly allow a physical system to relax. An example of this is a set of magnets. As the magnets are cooled down, the rate of flipping slows down; however, as that occurs, the influence of the direction of the neighboring magnets becomes more substantial. The relevance to D-Wave? D-Wave's computer pretty much does this. So, is it quantum or not? Why the difference?
Physique quantique : la première "molécule" de lumière
Assembler deux photons est quelque chose de totalement inédit à l'échelle subatomique, où l'individualisme des particules est de mise. C'est pourtant l'exploit réalisé par Ofer Firstenberg, de l'université Harvard (Cambridge, Etats-Unis), Thibault Peyronel (MIT, Cambridge) et leurs collèges. Ils ont publié la recette dans le magazine Nature du 25 septembre. Dans un nuage d'atomes En premier lieu, expédier un photon dans un nuage d'atomes de rubidium ultrafroid (un millième de degré seulement au-dessus du zéro absolu, -273°C). Les photons se rapprochent... Seulement, quand un atome se trouve excité par un photon, il devient insensible aux charmes du second. PERSPECTIVES. Une autre expérience : quand deux magnons se rencontrent...
Optical transistor switches states by trapping a single photon
Optical connections are slowly replacing wires as a means of shuffling bits in between systems—there are already plans afoot to have different components within a single system communicate via an optical connection. But, so far at least, all the processing of those bits is taking place using electrons. Yesterday's edition of Science includes a demonstration of an all-optical transistor that can be switched between its on and off states using a single photon. The work relied on a cold gas of cesium atoms. The cloud of atoms was placed between two closely spaced, extremely efficient mirrors—a setup that's called an optical cavity. What happens when you send in a photon that is at the right energy to correspond to the difference between one of the ground and excited states? Normally, the atoms start out in the lowest energy ground state, and a photon would place them in the corresponding excited state. Let's focus on that second wavelength of light.
