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Comment by NSAID | Hacker News Reader

>The team managed to send information from one chip to another instantly without them being physically or electronically connected

Doesn't current quantum teleportation require optical connectivity because the state transfers along photons?

The abstract says

>Here, we report the demonstration of chip-to-chip quantum teleportation and genuine multipartite entanglement, the core functionalities in quantum technologies, on silicon-photonic circuitry

So while there may not necessarily be a phsyical connection this does require line-of-sight by my read, and "silicon-photonic circuitry" sounds like this is all on one physical board.

I guess I don't understand how this is "two different chips" as the article claims. Did they use two photomasks? Baby steps, I suppose.

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Any form of quantum "teleportation" requires that the two chips first share a pair of entangles particles. Usually this is done by making the two entangled particles on one of the chips and sending one of the particles to the other chip. Usually the particles are photons for engineering reasons.

The quantum teleportation happens after that. Once the particles are entangled, you can destroy yours in a very particular way that forces the other particle to instantaneously become either a copy of the particle you destroyed (i.e. its state is the same) or the opposite of the particle you destroyed (i.e. its state is something like a boolean negation). Only you know which one happened (you learn that when you destroy your particle) and need to send one bit of classical information to the other chip in order for it to know as well.

In other words, you can transmit one bit of classical information and sacrifice one entangled pair to "teleport" one qubit of quantum information.

It is called teleportation because the quantum information never actually physically moved, rather it instantaneously went to the other chip. To know how to use it, you still need that classical bit to be transmitted in order to know whether the quantum information underwent a boolean negation.

I'm still so confused. I understand what a photon is (ish... I understand it can behave as a particle or wave, but in this case it is a "particle"). How do you "observe" a single photon? How do you "destroy" a single photon "in a particular way"? Heck, how to do keep something moving at the speed of light stuck inside a chip? Create a fiber optic loop somehow? How is the photon introduced into the loop?

Typically (for polarization qubits) a combination of waveplates, polarizing beam splitters and single-photon detectors (avalanche photodiodes, photomultipliers, or superconducting nano-wire detectors) are used to measure the qubit state. These detectors absorb the photons and turn them into detectable electrical signals. It is also possible to detect photons without destroying them (non-demolition measurement). However, this is much more difficult to do and leads to exactly the same results. After the measurement, the photon is no longer in a superposition state and is no longer entangled with the other one.

There is number of techniques for storing photon qubits. The easiest way is to send the light through a very long optical fiber spool. However, the achievable delay is limited due to absorption in the fiber. It is also possible to transfer the photon state onto a different system, such as a single ion or a superconducting qubit. Then the state of that system can later be measured.

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