Experimental Refutation of Real-Valued Quantum Mechanics under Strict Locality Conditions

Certification of non-classicality in all links of a photonic star network without assuming quantum mechanics

“…On the experimental side, we have shown that a six-photon network with multi-qubit entanglement swapping can be implemented at a sufficiently high quality and efficiency to pass these comparatively demanding tests of classicality. Nevertheless, our experiment leaves open the detection and locality loopholes, but recent experiments based on the simplest network 28 , 51 , 52 offer a potential avenue towards closing the latter loophole also for larger networks by carefully synchronising the signals from the independent sources. Similarly, more stringent implementations of independent sources, that do not rely on the quantum-inspired idea of a randomised phase, have been implemented separately 34 , 53 , 54 and their incorporation into the larger network considered here and beyond is a natural next step.…”

Experimental full network nonlocality with independent sources and strict locality constraints

“…In each source, a pulse pattern generator (PPG) sends 250 MHz trigger signals to drive a distributed feedback (DFB) laser such that its electric current switches from much below to well above the lasing threshold, indicating that the phase of each generated pump pulse is randomized [32]. In this way, we erase any quantum coherence between the pump pulses and disconnect the two SPDC processes on each experimental trial, thus closing the sourceindependence loophole under the reasonable assumption that hidden variables are created together with state emission (further details see [19,30]).…”

“…2(d)), where the measurement choice depends on random bits produced from private fast quantum random number generators (QRNGs) [29]. All random bits from the QRNGs pass the NIST randomness tests [33] (for more details, see [19,30,34]). All setting results and detections are locally recorded by their time-to-digital converters that are fed with Bob's timestamps information.…”

“…We confirm the space-time configuration and characterize the delays of all relevant events, namely: (1) emission (S 1 and S 2 ), i.e., the photon creation events in the sources; (2) the choice of measurement setting (QRNG A and QRNG C ), i.e., completing the quantum random number generation at Alice's and Charlie's nodes for choosing their measurements; and (3) the measurement (M A , M B , and M C ), i.e., finishing the single photon detection by Alice, Bob, and Charlie. In the experiment, the time reference to syn-chronize all events is set to the 12.5 GHz internal microwave clock of the PPG in source S 1 [30]. By employing QRNG and space-like separating setting choice and measurement on one side from the measurement on other sides, we close the locality loophole.…”

“…(b), By pumping a periodically poled MgO doped lithium niobate (PPMgLN) crystal in a Sagnac loop, photon pairs in the state |ϕ i = cos 2θi|HH + sin 2θi|V V are created via SPDC in each source, where θi is the angle of HWPi mounted on a motorized rotator. The pulse pattern generator (PPG) in S1 acts as a master clock for synchronizing all devices (see[19,30] for details). (c), Bob performs a partial Bell state measurement[31] and his photon detection events are real-time analyzed and recorded by a field-programmable gate array (FPGA).…”