Our loophole-free Bell test has been awarded the Ehrenfest Prize for best publication on the foundations of quantum mechanics. Below: Tim receiving the certificate from Caslav Brukner in Vienna.
Because quantum states are extremely fragile, large-scale quantum information processing is impossible without quantum error correction. In our latest publication in Nature Communications we realize active quantum error correction based on non-destructive measurements and real time feedback. This experiments marks the first time that quantum states are continuously protected by repeatedly detecting errors and actively corrected through classical logic and real time feedback, essential elements of fault-tolerant quantum computations.
The work was covered by several media, such as the volkskrant, tweakers.net and BNR radio, and even drew the attention of the Dutch royal family! See the videos and cartoon below for a basic explanation of quantum error correction.
Cartoon version of the experiment. (1) A logical quantum bit is encoded in three physical qubits (nuclear spins). (2) Errors are detected through non-destructive stabilizer measurements using an ancilla qubit (electron spin). (3) Errors are corrected through fast real-time feedback. Steps 2 and 3 are repeated in order to continuously protect the quantum state. Image by Wolfgang Pfaff, edited by Julia Cramer.
Our loophole-free Bell test was picked as a top 10 scientific breakthrough of 2015 by the magazine Science. Ultimately we lost out on the number 1 spot to CRISPR, the powerful genome editing technique. In the internet voting by the public, the New Horizons missions images of Pluto took first place, with our Bell test coming in 5th!
Just a few days later Nature selected our experiment as one of the science events that shaped 2015!
The renovation is finished and all three new labs look great (B-56, B-58 and B-60). Next step: constructing the experiments and doing science (after cleaning of course).
Lab warming party:
The before photos:
We think it is quite an improvement!
Our loophole-free Bell test has now been published in Nature. In this experiment performed at the Hanson lab we entangled two nitrogen-vacancy (NV) centers in diamonds placed in laboratories on opposite sides of the TU Delft campus (1.3 kilometer). We then used this entanglement to demonstrate a violation of Bell's inequality. Because the NV center spins were measured with high accuracy and because the complete measurement (choice of measurement basis, spin readout, storage of result in classical electronics) was performed in a time so short that no communication between the labs was possible, the experiment closes all loopholes that were present in previous experiments.
Our results reject the hypothesis that nature obeys the principle of local causality (or local realism), providing the strongest evidence yet that the world is fundamentally non local. The only remaining ways to save the local casual worldview is to invoke that the measurement choice was already determined at an earlier time or that the results stored were still altered after they were saved in the classical computers. Such theories can be further restricted in future experiments - most excitingly by using humans on earth and on the moon/in space to select the measurement settings and record the data - but can never be completely excluded.
The result made quite a splash in the media and was even featured on the cover of the New York Times. A good place to start is the coverage by the economist and two of the features by Nature (first, second).
This experiment was based in the Hanson lab at QuTech and is a collaboration with the groups of Stephanie Wehner (QuTech), Morgan Mitchell (ICFO), Valerio Pruneri (ICFO) and Matthew Markham and Daniel Twitchen (Element Six).