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This quantum ruler is the latest win against the many ‘nevers’ of quantum science

At a certain point, it looked like light was going to screw us. Its wavelengths, as we were able to create and use them, were in many cases too large for our purposes — even in the smallest range. Now, complex manipulation of light allows processors to be etched with details far smaller than the wavelength of the light doing the etching, which is a hurdle many thought (with good reason) would be impossible to get over.

Manipulation of entangled photons is another example of a supposedly impossible goal. Yet today, high-level quantum experiments regularly use entanglement as a tool to make even larger discoveries. Quantum weirdness has a way of surprising even those who study it; think you’ve got a handle on the limits of its seeming contradictions, and you’ll almost certainly be surprised in just a few years’ time.

Now, we’ve got yet another example from Russian scientists at MIPT and the Russian Quantum Center, using advanced manipulation of quantum states to overcome a seemingly insurmountable problem with transmitting quantum information over large distances: It’s extremely fragile. The ability to use quantum information in many cases requires the use of quantum interference. That means the individual attributes of the photons being transmitted can be combined at some future point to observe the effect, and from this combined effect discern extremely tiny changes in either of the contributing waves. In order for that to work, the transmission medium (say, a fiber-optic cable) has to be able to keep the states of both transmissions perfectly stable. If there’s any loss of information, the entanglement breaks, and the instrument doesn’t work.

noon states 2In the LIGO gravitational wave detector, this sort of quantum interference scheme has been made to work over distances like several kilometers — it can measure “atom-scale” differences in the path-length of a laser, but its physical size is limited by that constraint of requiring “lossless” transmission media past a certain critical path-length. The new Russian technology has found a way around this problem. They haven’t gone straight through it, creating a perfectly lossless transmission medium or eliminating the loss-sensitive nature of entanglement, but around it by exploiting the odd abilities of quantum particles.

Basically, these researchers swap the entanglement state of two distant particles with the states of two other particles, closer to the point of transmission and thus having traveled a smaller distance through the “lossy” media. By creating a “N00N state” involving their two particles of interest, the team can jump their entangled state far down the line — as in, up to a hundred kilometers, or many times the size of LIGO.

quantum dots head

It’s not just the search of gravitational waves that will be affected by this; the use of super-advanced interferometers will probably be useful to the study of dark matter as well, or potentially time dilation. It has the potential to be relevant to any field where tiny, tiny changes in path or distance could be relevant. And quantum communications technologies might not be too far away — especially if these sorts of breakthroughs can improve its fidelity in data transmission.

We used to lose a huge proportion of data over the telegraph lines. It was fundamental research like this that increased the signal to noise ratio, and it’s fundamental research like this that could do it again.

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