Scientists have transferred quantum information fron an atom to a photon

Physicists at the University of Innsbruck in Austria have succeeded in transferring quantum information from an atom to a photon, a process considered vital in the construction of a quantum computer. The discovery would allow quantum computers to exchange data at the speed of light along optical fibres.

Lead researcher on the project Tracy Northup told Humans Invent, “What we’ve done is to show that you can map quantum information faithfully from an ion onto a photon.” Northup’s team used an “ion trap” to produce a single photon from a trapped calcium ion with its quantum state intact using mirrors and lasers.

Humans Invent spoke with Tracy Northup about her work in quantum computing and the possibility of a quantum internet.

What is a quantum computer and why would we need them?

A classical computer encodes information in one of two states, 0 or 1. A quantum computer replaces this bit with a quantum bit or qubit; in a qubit, 0 and 1 are states of a quantum-mechanical system, such as the energy of an atom’s outermost electron, or the polarization of light. A quantum bit can be either 0 or 1, but it can also be in a superposition of 0 and 1 at the same time, so it offers a very different way to store and process information.

A quantum computer replaces the bit for a qubit

There are certain types of problems that are very hard on a classical computer that could be solved much more efficiently on a quantum computer. One famous example is factoring large numbers because the difficulty of this problem is the basis for RSA encryption (an algorithm for public-key cryptography).

Why does quantum information have to be transmitted by optical channels?

It doesn’t have to be, but that’s the idea that seems to make the most sense. Photons travel at the speed of light and they are also well isolated from their environment, so it’s highly likely that the information you put in will come out the other end and not get lost along the way. Ions are great for quantum computation but no one wants to think about transporting ions over long distances because that would be very slow and cumbersome.

What can quantum computers do that today’s computers can’t?

If we had quantum computers with thousands of quantum bits, they could do specific tasks, like factoring large numbers or a database search, faster. Since factoring is the basis for today’s encryption that generates a lot of interest.

But currently in the lab, the state of the art is tens of quantum bits, not thousands. So what many people are excited about as an intermediate goal is quantum simulation, that is, building not an all-purpose quantum computer but a very specific device that is tailored to simulate another quantum system, such as molecular structure, or superconductivity. It’s quite computationally intensive to simulate quantum systems on classical computers and so it may be possible to do simulations that are beyond the reach of classical computers.

What would be the benefits of a network of quantum computers or a quantum internet?

One benefit is quantum cryptography. Over a quantum network, you could distribute secure information. In fact, quantum key distribution systems are already available commercially.

You could use quantum teleportation protocols to transmit data from one site to the other

Another benefit would be distributed quantum computing. By linking together smaller computers, you could carry out larger, more powerful computations.

Could you also transmit data using quantum entanglement?

Yes. Instead of mapping information from atom to photon to atom, you could also entangle each of two remote atoms with a photon and then, based on measurements of those photons, generate entanglement between the atoms. Finally, you could use quantum teleportation protocols to transmit data from one site to the other.

How far are we from developing quantum computers for everyday use?

Well, on one hand, quantum computers would probably be for very specialized tasks rather than everyday use, although I know they said that about classical computers!

In a nutshell, no one really knows. Of course, we’d love to have quantum computers, but I think what drives most researchers in the field is not necessarily this far-off goal but the kinds of strange things you learn along the way. Scott Aaronson expressed this really nicely in an essay he wrote for the NY Times a few years ago.

Image credit: R.T. Wohlstadter (shutterstock)

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