Title:Quantum Journal Club: Quantum imaging with undetected photons
Speaker: Panyu Hou Tsinghua University
Time: 2014-10-09 15:00-2014-10-09 16:00
Venue:FIT 1-222


Information is central to quantummechanics. In particular, quantum interference occurs only if there exists no information to distinguish between the superposed states. The mere possibility of obtaining information that could distinguish between overlapping states inhibits quantum interference1,2. Here we introduce and experimentally demonstrate a quantum imaging concept based on induced coherence without induced emission3,4. Our experiment uses two separate down-conversion nonlinear crystals (numberedNL1 andNL2), each illuminated by the same pump laser, creating one pair of photons (denoted idler and signal). If the photon pair is created in NL1, one photon (the idler) passes through the object to beimaged and is overlapped with the idleramplitude created in NL2, its source thus being undefined. Interference of the signal amplitudes coming from the two crystals then reveals the image of the object. The photons that pass through the imaged object (idler photons from NL1) are never detected, while we obtain images exclusively with the signal photons (from NL1 and NL2), which do not interact with the object. Our experiment is fundamentally different from previous quantum imaging techniques, suchas interaction-free imaging5 or ghostimaging6–9, because now the photons used to illuminate the object do not have to be detected at all and no coincidence detection is necessary. This enables the probe wavelength to be chosen in a range for which suitable detectors are not available.To illustrate this, we show images of objects that are either opaque or invisible to the detected photons. Our experiment is a prototype inquantuminformation—knowledge can be extracted by, and about, a photon that is never detected.

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