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Photons: our first state variable/状態変数としての光子

Photons: our first state variable/状態変数としての光子
Hi. We are here in the laboratory of Professor Akira Furusawa at the University of Tokyo. Professor Furusawa, thank you for joining us today. Sure. So the first thing we want to talk about, professor Furusawa’s group is one of the leading groups on the planet doing quantum computing using optical states, using photons and light. So first, tell me what’s a photon? Uhm, that is a tough question but, uh, first of all it is particle of light. Okay. And also, uh, light is wave. Um-hmm. So, it is rather complicated. Um-hmm. So a light has a nature of particle… Um-hmm. …and also wave. Just like other types of the quanta that we have been looking at so far. Okay.
And it also has a wavelength light, so it has a certain energy? Yeah. Okay. Right. Alright, so you are working with individual photons. One photon at a time… Right. …being a qubit. Okay. So how do you represent a qubit using a photon? How do you make data with it? There are two types. One is called a polarization qubit. In that case we use a single photon. Okay. And we use two polarization. Two polarizations. One is horizontal and another one is vertical. Okay. And Another type of qubit is called time-bin qubit. In that case, we use two pulses of light and single photon. So in that case, single photon exists in first pulse or a single photon exists in second pulse.
Okay. So that’s super position. Okay. So if it’s polarization that means that the light is vibrating in a particular direction? So either vertically or horizontally. Right. So that we might use this as our zero state and this as our one state… … or maybe the other way around. Yeah. And if they are time-bin photons, let’s see, so that means that a photon can either arrive early or it can arrive late. Right, yeah. So you might say the early state is your zero state… And the late state is your one state. Something like that. Is that correct? Yeah. Okay. And they run, in that case they run through the same physical path. They run through the same part of your system.
Yeah. Same light beam. Okay, great. They are part of the same light beam. So I think that gives you an idea of what the state variable for photonic systems is, working with individual photons. Thank you. Sure.





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