Experimental test of nonclassicality with arbitrarily low detection efficiency

We theoretically introduce and experimentally demonstrate the realization of a nonclassicality test that allows for arbitrarily low detection efficiency without invoking an extra assumption of independence of the devices. Our test and its implementation is set in a prepare-and-measure scenario with an upper limit on the classical communication capacity of the channel through which the systems are communicated. The essence for our test is the use of two preparation and two measurement devices, which are randomly paired in each round. Our work opens the possibility for experimental realizations of nonclassicality tests with off-the-shelf technology.

Figure 1

Semi-device-independent implementation in a prepare-and-measure scenario. Preparation device communicates a system depending on its inputs. The message is encoded in a system with an upper bound on the dimension. The measurement device's output depends on its inputs and the received message.

Figure 2

Parallel RAC scenario consisting of two preparation devices, $P^0$ and $P^1$, and two measurement devices, $M^0$ and $M^1$. The pairing choice between the senders and receivers devices depends on the value of random variable $x$. Here, the solid line corresponds to $x=0$, and the dotted line to $x=1$.

Figure 3

Experimental setup. Information is encoded into two spatial-photonic modes. The preparation devices $P_i$ ($i=0,1$) consist of a heralded single photon source that emits horizontally polarized photons which, after passing through a half-wave plate (HWP) oriented at an angle ${\theta }_i$, can be prepared in the required protocol states. The measurement devices $M_i$ consist of a HWP oriented at an angle ${\phi }_i$, polarization beam splitter (PBS), single photon detectors $D_{ij}$. The pairing of the preparation and measurement devices is performed with help of adjustable HWP plates and PBSs.