Interaction-free measurement of multiple objects using a universal integrated photonic processor

Abstract

The phenomenon of interaction-free measurement (IFM) enables the probabilistic detection of an absorbing object with reduced photon absorption. We report the experimental implementation of a simultaneous IFM of multiple objects using a single quantum probe on the cloud-based Ascella photonic processor of company Quandela. We demonstrate sequential IFM of up to 5 objects using a single photon, significantly extending the original IFM scheme for a single object. The experimental error-mitigated results confirm the theoretical predictions for this sequential IFM setup, and demonstrate a practical approach to scaling IFM to more complex quantum interrogation tasks.

Figures (14)

• Figure 1: The Elitzur-Vaidman (EV) setup for an interaction-free measurement, based on a Mach-Zehnder interferometer. Single photons are input on the left in mode 0, and exit towards photodetectors $D_0$ or $D_1$. The beamsplitters BS of reflectivity $R$ act on the incoming optical modes according to eq.\ref{['eq:BS']}. The interferometer is configured for destructive interference in output mode 1 in the absence of obstruction. When an opaque object is placed in one of the arms, for example, the bottom one, detection at $D_1$ signals the presence of the object in the device, without an interaction occurring between it and the photon.
• Figure 2: Generalized setup for single object interaction-free measurement. Any $m$-mode interferometer implementing a generic unitary transformation $U_m$ followed by its inverse $U_m^{\dagger}$ can be used to perform the interrogation of a single object, placed in any mode $k$ between the two unitaries. If single photons are input in mode $j$, they always exit towards photodetector $D_j$ at the output when the object is absent. A detection at any output mode but $j$ heralds the presence of an object in an undetermined arm of the interferometer.
• Figure 3: Filatov-Auzinsh proposal for the simultaneous IFM of two objects. The outputs of the EV scheme of Fig.\ref{['fig:EV']}, used for the IFM of object 1, are each redirected to one of two additional EV units, with spatially overlapped optical modes so that they can both interrogate object 2. Single photons are input at the top port of the leftmost EV unit. If detection occurs at photodetector $D_12$, the presence of both objects is simultaneously signalled with no interaction. Detections at $D_1$ or $D_2$ give partial information on the presence of object 1 or object 2, respectively. $D_0$ is the null outcome, giving no information on either object.
• Figure 4: (a) Scheme for the simultaneous interaction-free measurement of two objects. Each EV box corresponds to the scheme in Fig.\ref{['fig:EV']}. Detection at $D_2$ only occurs when there is one object inside each box. This setup can be straightforwardly generalized to any number of objects. (b) Generalized scheme for the simultaneous interaction-free measurement of $n$ objects. Each EV box corresponds to the setup in Fig.\ref{['fig:EV']}, with some choice of the beamsplitters reflectivity $R$.
• Figure 5: Extension of the scheme illustrated in Fig.\ref{['fig:n_objects']} for 15 objects, in a graph representation. Each node represents an EV unit, with edges representing input-output interferometer connections between them. A 16-mode interferometer can fit the quantum interrogation modules of 15 objects, in 4 layers of pairs of beamsplitters. Coloured sequences of nodes represent sets of objects interrogated by each unit which can be detected counterfactually with a single probe.