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2021-11-09, 15:00: Dr Colm Bracken (Maynooth University)

Untangling the Delayed-Choice Entangled Quantum Eraser – Could the KIDs offer the solution?

Speaker: Dr Colm Bracken, Maynooth University

Abstract:  In this proposed update to the DCQE (delayed-choice quantum eraser) set-up, we propose to use photon-counting MKIDs as the detector technology at both the primary/interference measurement plane and at the secondary/‘eraser’ plane. A DCQE set-up allows one to investigate the strange consequences of the classic double-slit experiment by exploiting the effects of quantum entanglement. As claimed by the authors of previous studies, e.g. (Kim, et al. (2000), the DCQE allows the ‘which-path’ or ‘both-path’ information of a signal photon to be erased or marked by measuring its entangled twin in one of two ways, even after the detection of the signal photon. Previous experiments reported in the literature used a moveable detector to raster-scan across the plane of the interference pattern. That approach relied on building-upsufficient photon statistics over time spans of many seconds to show the wave-like or particle-like pattern on the detector plane. By substituting the sensor on the far-field image plane with an array of optical/near-IR MKIDs, deeper insights into the physics involved in the DCQE can be gained, enabled by an MKID array’s ability to simultaneously monitor the full image plane with < microsecond time-resolution. The MKID array’s ability to timestamp (and spatially stamp) the arrival of individual photons to ≈ 100 nanosecond precision, will allow the moment-by-moment analysis of the entanglement and decoherence processes. It will also be shown that an MKIDs-based DCQE can be used to settle a measurement paradox, which is essentialy an alogue of the famous Grandfather paradox. This curiosity is realised by introducing a feedback loop into the DCQE apparatus. It seems that the common retrocausality interpretation of this experiment cannot predict what will happen when the measurements will be performed. Clearly the contradiction itself will not manifest, for what would that mean? Would the world end in a poof? Would an error message pop up, crashing the simulation that is our reality? Certainly not (we hope). But then what will happen when we carry-out the measurments? I look forward to presenting my work, and discussing the implications with my emminent colleagues at DIAS on November 9th.