The First Experiment: Independence

Bettina Just

René Schwonnek, Koon Tong Goh, Ignatius William Primaatmaja +4 more

Device-independent quantum key distribution (DIQKD) is the art of using untrusted devices to distribute secret keys in an insecure network. It thus represents the ultimate form of cryptography, offering not only information-theoretic security against channel attacks, but also against attacks exploiting implementation loopholes. In recent years, much progress has been made towards realising the first DIQKD experiments, but current proposals are just out of reach of today's loophole-free Bell experiments. In this Letter, we close the gap between the theory and practice of DIQKD with a simple variant of the original protocol based on the celebrated Clauser-Horne-Shimony-Holt (CHSH) Bell inequality. In using two randomly chosen key generating bases instead of one, we show that the noise tolerance of DIQKD can be significantly improved. In particular, the extended feasibility region now covers some of the most recent loophole-free CHSH experiments, hence indicating that the first realisation of DIQKD already lies within the range of these experiments.

Hiroki Takesue

I report the first Hong-Ou-Mandel experiment using two photon pairs in the 1.5-μm band that are generated in two independent dispersion shifted fibers. A quantum interference with 53% visibility was observed.

R. Casalbuoni, G. Domokos, Susan Kovesi-Domokos +1 more

Helmut S. Schmidt

A psychokinetic (PK) effect--a mental influence on the outcome of chance processes--was first reported by Louisa and J. B. Rhine (Rhine & Rhine, 1943) from experiments with dice. Through the introduction of electronic random number generators based on quantum randomness (Schmidt, 1971), the experiments became more easily accessible and even more challenging to physicists. Today, a large number of successful PK experiments with random number generators have been reported (Radin & Nelson, 1989). It has not yet been possible, however, to stabilize and strengthen the statistically weak effects so that they can be easily demonstrated on demand. The discovery of PK effects on prerecorded random events (Schmidt, 1976) did not make the gathering of data less arduous, but it permitted the inclusion of independent observers who, with little investment of time and effort, could obtain first-hand evidence for any PK effects that might occur. All five experiments to be discussed here included such independent observers. PK Tests with Prerecorded Events and Independent Observers In a typical PK experiment, a random number generator produces a binary random sequence that the subject tries to bias in a certain manner. Let us take, for example, the case where the random generator produces in each test run a sequence of 100 binary events displayed as a sequence of 100 red (for a 0-bit) and green (for a 1-bit) light flashes, while the subject is instructed to mentally enforce the appearance of more red than green flashes. The sequence of red and green signals is stored on floppy disk, and a score that is measured by the difference between the numbers of red and green signals is displayed and recorded at the end of the run. The arrangement for an experiment with prerecorded random events is similar, but there is a time delay between the generation of the random events and their display to the subject. First, the random signals for a large number of test runs are generated and recorded on floppy disk. Days or months later, the stored signals are translated by the computer into a corresponding sequence of red and green light flashes while the subject tries to mentally enforce the appearance of more red than green signals. Experiments have shown that selected subjects can succeed in this arrangement (Schmidt, 1976, 1987), provided that the prerecorded events have not been inspected by anybody before the subject makes the PK effort. To let an independent observer participate in the experiment, we prerecord the bit sequences for all test runs planned for the experiment, and we let a computer make a printout of the scores for all the test runs. Being careful that nobody can observe the scores, we send a sealed copy of the printout to the independent observer. Leaving the printout sealed, the independent observer randomly specifies for each test run whether the subject's PK effort should be aimed at a high score (excess of red signals in the example) or a low score (excess of green signals). In the subsequent PK test sessions, the subject follows for each test run the independent observer's assignments, aiming for an excess of red or green signals, respectively. At the end of the experiment, the independent observer opens the sealed printouts. If the subject's effort was successful, the independent observer can confirm this first-hand by a tendency of the scores to point in the directions (positive or negative) that he had randomly specified. Because the independent observer had randomly assigned the directions, he or she can be certain that no such systematic tendency should occur (in the absence of the claimed anomaly). Using an appropriate statistical method, the independent observer can assess the significance of such a tendency without having to consider the reliability of the experimenter and his procedures. Test Arrangement with Distant Subjects The five experiments under discussion followed this general outline with minor variations. …