Entanglement is of central importance for the new quantum technologies of the 21st century. A German-Austrian research team is now presenting the largest entangled quantum register of individually controllable systems to date, consisting of a total of 20 quantum bits. The physicists in Innsbruck, Vienna and Ulm are pushing experimental and theoretical methods to the limits of what is currently possible.

Some of the new quantum technologies ranging from extremely precise sensors to universal quantum computers require a large number of quantum bits in order to exploit the advantages of quantum physics. Physicists all over the world are therefore working on implementing entangled systems with more quantum bits. The record is currently held by Rainer Blatt's research group at the Institute of Experimental Physics at the University of Innsbruck. In 2011, the physicists entangled 14 individually addressable quantum bits for the first time and thus realized the largest completely entangled quantum register. Now, a research team led by Ben Lanyon and Rainer Blatt at the Institute of Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences, together with theorists from the University of Ulm and the Institute of Quantum Optics and Quantum Information in Vienna, has achieved controlled multi-particle entanglement in a system of 20 quantum bits. The researchers were able to detect genuine multi-particle entanglement between all neighbouring groups of three, four and five quantum bits.

**Genuine multi-particle entanglement**

Physically, entangled particles cannot be described as individual particles with defined states, but only as a complete system. It is particularly difficult to understand entanglement when numerous particles are involved. Here, a distinction must be made between the entanglement of individual particles and genuine multi-particle entanglement. This can only be understood as a property of the overall system of all particles concerned, and cannot be explained by a combination of the subsystems being entangled.

At the Institute of Quantum Optics and Quantum Information in Innsbruck, the team of physicists used laser light to entangle 20 calcium atoms in an ion trap experiment and observed the dynamic propagation of multi-particle entanglement in this system. "The particles are first entangled in pairs," describes Lanyon. "With the methods developed by our colleagues in Vienna and Ulm, we can then prove the further spread of the entanglement to all neighbouring particle triplets, most quadruplets and a few quintuplets.

These detection methods were developed by Martin Plenio's research group at the University of Ulm and Marcus Huber's team at IQOQI Vienna. "We have chosen a MacGyver approach," says first author Nicolai Friis. "We had to find a way to detect multi-particle entanglement with a small number of feasible measurement settings."

The researchers took a complementary approach: The group around Huber and Friis used a method that only requires a few measurements and whose results can be easily evaluated. In this way, the entanglement of three particles could be demonstrated in the experiment. The theorists from Ulm used a more complex technique based on numerical methods. "Although this technique is efficient, it also reaches its limits because of the sharp increase in computing effort due to the number of quantum bits," says Oliver Marty from Martin Plenio's research group. "That's why the usefulness of this method also came to an end with the detection of real five-particle entanglement."

**A big step towards application**

"There are quantum systems such as ultra-cold gases in which entanglement between a large number of particles has been detected," says Nicolai Friis. "However, the Innsbruck experiment is able to address and read out every single quantum bit individually." It is therefore suitable for practical applications such as quantum simulations or quantum information processing. Rainer Blatt and his team hope to increase the number of quantum bits in the experiment. "Our medium-term goal is 50 particles," he says. "This could help us solve problems that the best supercomputers today still fail to accomplish."

The methods developed for the ion trap experiment in Innsbruck will be used more widely, the physicists in Ulm and Vienna are convinced. "We want to push the boundaries of our methods even further," say Friis and Marty. "By exploiting symmetries and focusing on certain observables, we can further optimize these methods to detect even more extensive multi-particle entanglement.

The research was published in *Physical Review X*.

**Explore further:**
14 quantum bits: Physicists go beyond the limits of what is currently possible in quantum computation

**More information:**
Nicolai Friis et al, Observation of Entangled States of a Fully Controlled 20-Qubit System, *Physical Review X* (2018). DOI: 10.1103/PhysRevX.8.021012

## xinhangshen

Therefore, the wave property in the particle-wave duality is more likely the result of the wave of aether rather than the wave of probability which is not a physical substance and can't vibrate to become waves, but the wave of aether generated by the motion of the particle always accompanies the motion of each particle.

## Da Schneib

## mackita

## Da Schneib

Do better, physorg.

On edit: luckily, the paper is not paywalled. Just follow the link at the end of the article above.

## xinhangshen

Don't behave so naive and ignorant please!

## mackita

But the same effects occurs at short distances and this effect is called entanglement. This is why the entanglement records are made with collinear bodies (1, 2, 3...)

## mackita

## mackita

## Da Schneib

## xinhangshen

It is you who is ignorant about what I have studied such as the well-known M-M experiment.

## mackita

## mackita

Modern physicists elevated the nondetectability of aether drag into third level once they arranged Michelson-Morley experiment not within free vacuum but inside material environment like the sapphire. Under this particular arrangement even if some residual drag of aether would exist, then from the very same reason the aether would get dragged by sapphire too resulting into zero net drag. Such an experiments just illustrate complete misunderstanding of not only environment and waves concepts - but also reference frame concept.

## Da Schneib

## szore88

## xinhangshen

## Da Schneib

If you can't explain how something works, you don't understand it. If you don't understand something, you can't possibly have any valid reason for declaring it to be incorrect.

I knew I had you on ignore for some reason. Now I remember what it is.

## xinhangshen

Please be aware that M-M experiment only denies a rigid aether, but what I have found is a fluid aether.