A controlled multiparticle entanglement in a system of 20 quantum bits has been achieved by a research team at the Institute of Quantum Optics and Quantum Information (IQOQI) in Innsbruck, together with researchers from the University of Ulm and IQOQI Vienna. The researchers were able to detect genuine multiparticle entanglement between all neighboring groups of three, four, and five quantum bits. The new record surpasses the previous entanglement record of 14 individually addressable quantum bits, achieved in 2011 by a team at the Institute of Experimental Physics at the University of Innsbruck. Conceptual picture of the new exotic quantum states that have been generated in Innsbruck. The generation of quantum entanglement in a string of 20 single atoms is shown. Entanglement between neighboring atom pairs (blue), atom triplets (pink), atom quadruplets (red), and quintuplets (yellow) was observed before the system became too complex to characterize with existing techniques. Courtesy of IQOQI Innsbruck/Harald Ritsch. IQOQI Innsbruck physicists used laser light to entangle 20 calcium atoms in an ion trap experiment and observed the dynamic propagation of multiparticle entanglement in this system. “The particles are first entangled in pairs. With the methods developed by our colleagues in Vienna and Ulm, we can then prove the further spread of the entanglement to all neighboring particle triplets, most quadruplets, and a few quintuplets,” said research team leader Ben Lanyon. Researchers developed new detection methods to observe and characterize the entangled states. “We had to find a way to detect multiparticle entanglement with a small number of feasible measurement settings,” said researcher Nicolai Friis, IQOQI Vienna. Researchers at Vienna used a method that only requires a few measurements and whose results can be easily evaluated. Using this method, the entanglement of three particles could be demonstrated in the experiment. Researchers from Ulm used a more complex technique based on numerical methods. “Although this technique is efficient, it also reaches its limits due to the sharp increase in computing effort due to the number of quantum bits. That’s why the usefulness of this method also came to an end with the detection of real five-particle entanglement,” said researcher Oliver Marty from the University of Ulm. Because the Innsbruck experiment was able to address and read out every single quantum bit individually, it could be appropriate for practical applications such as quantum simulations or quantum information processing. The team hopes 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 the best supercomputers today still fail to accomplish,” said research team leader Rainer Blatt, who led the group that achieved the previous entanglement record of 14 individual qubits. The research was published in Physical Review X (doi:10.1103/PhysRevX.8.021012).