Some of the new quantum technologies ranging from extremely precise sensors to universal quantum computers require a large number of quantum bits to exploit the advantages of quantum physics. Hence physicists around the world are working to implement entangled systems with more and more quantum bits.
Now, a team of scientists led by Ben Lanyon and Rainer Blatt from the Institute for Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences, together with theorists from the University of Ulm and the Institute for Quantum Optics and Quantum Information in Vienna have achieved the most accurate chemical reaction in the world, joining just two atoms of elements that would not normally make a molecule. The two elements, sodium and cesium, produced an interesting multi-particle alloy-like molecule in a 20-bit quantum system. The researchers were able to detect genuine multi-particle entanglements between all neighboring groups of three, four, and five quantum bits.
Genuine multi-particle entanglement can only be understood as a property of the global system of all the particles involved and is not explained by a combination of the subsystems becoming entangled.
Here physicists have used laser light to entangle 20 calcium atoms in an ion trap experiment, observing the dynamic propagation of multi-particle entanglement in this system.
The funny thing is that when you want to combine really exotic elements, scientists need to get creative , because sodium (Na) and cesium (Cs) are in the same group on the periodic table and, as we will remember from school, this means that they tend to have similar reactive properties. They also don’t tend to collide with each other and bond easily like a molecule, which is really a shame, as the polarized electrical properties of a NaCs molecule would make it very useful for storing superposition states of quantum “qubits” that can also easily interact. with other components. Hence they needed to be a bit … imaginative.
“We have chosen a MacGyver approach ,” says Nicolai Friis with a smile. “We had to find a way to detect multi-particle entanglement with a small number of feasible measurement setups.” And it is that, improbable does not mean impossible: if these two atoms are close enough with the right energy, a connection can be formed.
A big step
“There are quantum systems such as ultracold gases in which an entanglement between a large number of particles has been detected. However, the Innsbruck experiment can address and read each quantum bit individually “, clarifies Friis. Therefore, it is suitable for practical applications such as quantum simulations or quantum information processing.
To achieve this perfect mix of energy and timing , the researchers held individual atoms overlapping magneto-optical traps and threw photons at them to cool them down to a fraction of a degree above absolute zero.
Meanwhile, they used a pair of tuned lasers to create an electrical effect, causing each atom to move towards the focus of each laser, as if they were drawn into two tractor beams from science fiction.
The result is a brief flicker of a bond between two atoms in the same quantum state.
The ultimate goal would be to adapt the creation of much more complex molecules, making use not only of their classical shapes but also creating tiny quantum components for the next generation of computing.
Rainer Blatt and his team hope to further increase the number of quantum bits in the experiment. “Our medium-term goal is 50 particles. This could help us solve problems that today’s best supercomputers still don’t.”
Referencia: Publication: Observation of entangled states of a fully controlled 20-qubit system. Nicolai Friis, Oliver Marty, Christine Maier, Cornelius Hempel, Milan Holzäpfel, Petar Jurcevic, Martin Plenio, Marcus Huber, Christian Roos, Rainer Blatt, and Ben Lanyon. Physical Review X 2018 DOI: 10.1103/PhysRevX.8.021012
Image credit: IQOQI INNSBRUCK / HARALD RITSCH
