Hance, Jonte R

Rarity, John G

English

We have developed a protocol for ghost imaging that is always exchange-free - while imaging an object, no light interacts with it. This provides both better visibility/SNR and less absorbed intensity than ghost imaging.<br/

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                          Hance, J. R., & Rarity, J. G. (2021). Exchange-Free Ghost Imaging. InOSA Optical Sensors and Sensing Congress 2021 (AIS, FTS, HISE,SENSORS, ES) (OSA Technical Digest; Vol. 2021, No. SW5F.5).Optical Society of America (OSA).https://doi.org/10.1364/SENSORS.2021.SW5F.5Peer reviewed versionLink to published version (if available):10.1364/SENSORS.2021.SW5F.5Link to publication record in Explore Bristol ResearchPDF-documentThis is the author accepted manuscript (AAM). The final published version (version of record) is available onlinevia Optica Publishing Group (formerly OSA) at https://doi.org/10.1364/SENSORS.2021.SW5F.5 . Please refer toany applicable terms of use of the publisher.University of Bristol - Explore Bristol ResearchGeneral rightsThis document is made available in accordance with publisher policies. Please cite only thepublished version using the reference above. Full terms of use are available:http://www.bristol.ac.uk/red/research-policy/pure/user-guides/ebr-terms/Exchange-Free Ghost ImagingJonte R. Hance, John RarityQuantum Engineering Technology Laboratory, Department of Electrical and Electronic Engineering, Universityof Bristol, Woodland Road, Bristol, BS8 1UB, UKjonte.hance@bristol.ac.ukAbstract: We have developed a protocol for ghost imaging that is always exchange-free -while imaging an object, no light interacts with it. This provides both better visibility/SNRand less absorbed intensity than ghost imaging. © 2021 The Author(s)In our recent paper [1], we introduced a new counterfactual ghost imaging scheme, where a ghost image isformed without the imaged object ever absorbing any photons. This scheme makes use of Salih et al’s always-counterfactual communication protocol [2], where Alice obtains a different result depending on whether or notBob blocks his side of a channel, without any chance of the photon having gone via Bob [3, 4] (which has evenled to protocols which send quantum information counterfactually [5–9]).Zhang et al previously combined Ghost Imaging with the Elitzur-Vaidman Bomb Detector [10] to create a formof Ghost Imaging where there is a chance that information is still received about the imaged object without anyphotons being absorbed by it [11]. However, the Elitzur-Vaidman Bomb Detector is at most 50% efficient, and isnot always necessarily counterfactual - there is a (reasonably high) chance the photon can go via the object beinginvestigated [12].By replacing the Elitzur-Vaidman object-detection system in Zhang’s protocol with Salih et al’s method forcounterfactual communication, we have created a protocol for ghost imaging that is always counterfactual - when-ever information is received about the imaged object, no photons have interacted with that object. Further, even incases when no information travels, far fewer photons go to the object than in either the standard ghost imaging orin the interaction-free ghost imaging case - reducing the energy absorbed by the object, and so potentially damagedone to that object by the imaging process.We now go over the specifics of our protocol, as shown in Fig.1. We create a pair of position-and-momentum-entangled photons, one horizontally polarised and one vertically polarised, by passing a pulsed pump laser througha spontaneous parametric downconversion (SPDC) crystal, before collimating the beam, and filtering out thepump. The photon pair is split at a polarising beamsplitter (PBS), with the V -polarised photon going through along optical delay to an Intensified Charge-Coupled Device (ICCD) camera, and the H-polarised photon goingthrough a run of Salih et al’s protocol, adapted so the object to be investigated is put in place of Bob’s blocker.The switchable mirrors allow the photon to cycle the correct number of times: the first for M outer cycles; and thesecond for N inner cycles per outer cycle. The polarisation separators subtly divert horizontally-polarised light,and directly transmit vertically-polarised light. The Half Wave Plates are tuned to implement a R̂y(θ) polarisation-mode rotation with θ of π/2M and π/2N respectively. The detector DL acts as our loss channels (which wepostselect against). After M outer cycles, the switchable mirror sends the photon to the optical circulator, whichsends it to the PBS. The path not being blocked by the object leads the photon to remain H-polarised, and so go toD0, leading to a coincidence measurement between that and the ICCD camera; however, the path being blockedleads to the photon becoming V -polarised and so going to D1, so coincidence measurement between that andthe ICCD. The use of multi-mode interferometers and (position-momentum) correlations between the entangledphotons enables multi-mode ghost imaging in this counterfactual set-up. Note, the polarisation separators ensure acommon path length for both H− and V -polarised components, while generating beam separations of the severalmillimetres. A further optimisation has photons going to DL can trigger a coincidence measurement with theICCD, treated as if it was a detection at D0, which does not affect the chance of photons interacting with theobject (photons only go to DL if the object doesn’t block the channel), and allows us to lower the number of outercycles to the minimum required (2) with no increase in loss.Even for low numbers of outer and inner cycles (M and N), our protocol gives a vast improvement over thesignal-to-noise ratio of standard ghost imaging - for instance, two outer cycles of 13 inner cycles gives double theequal-photon-absorption SNR of standard ghost imaging. Note, as N→ ∞, the probability of a photon interactingwith the object goes to 0, meaning SNRInt becomes infinitely larger than the SNR available with standard ghostimaging (if we’re willing to wait that long).We have given a protocol for ghost imaging in a way that is always counterfactual - while imaging the object,Fig. 1. Our Counterfactual Ghost Imaging Protocol, based on the combination of standard GhostImaging and a common-path interferometer version of Salih et al’s counterfactual communicationprotocol [3].no light interacts with that object. This extends the idea of counterfactuality beyond communication, showing howthis interesting phenomenon can be used for metrology. Given, in the infinite limit, no photons ever go to theimaged object, it presents a method of imaging even the most light-sensitive of objects without damaging them.Acknowledgements- We thank Hatim Salih, Alex McMillan and Will McCutcheon for useful discussions. Thiswork was supported by the University of York’s EPSRC DTP grant EP/R513386/1, and the Quantum Communi-cations Hub funded by the EPSRC grant EP/M013472/1.References1. J. Hance and J. Rarity, “Counterfactual ghost imaging,” arXiv preprint arXiv:2010.14292 (2020).2. H. Salih, W. McCutcheon, J. R. Hance, and J. Rarity, “Do the laws of physics prohibit counterfactualcommunication?” arXiv preprint arXiv:1806.01257 (2018).3. H. Salih, Z.-H. Li, M. Al-Amri, and M. S. Zubairy, “Protocol for direct counterfactual quantum communi-cation,” Phys. Rev. Lett. 110, 170502 (2013).4. Y. Cao, Y.-H. Li, Z. Cao, J. Yin, Y.-A. Chen, H.-L. Yin, T.-Y. Chen, X. Ma, C.-Z. Peng, and J.-W. Pan,“Direct counterfactual communication via quantum zeno effect,” Proc. Natl. Acad. Sci. (2017).5. H. Salih, “Protocol for counterfactually transporting an unknown qubit,” arXiv preprint arXiv:1404.2200v1(2014).6. H. Salih, “Protocol for counterfactually transporting an unknown qubit,” Front. Phys. 3, 94 (2016).7. H. Salih, “From a quantum paradox to counterportation,” arXiv preprint arXiv:1807.06586 (2018).8. H. Salih, J. R. Hance, W. McCutcheon, T. Rudolph, and J. Rarity, “Exchange-free computation on anunknown qubit at a distance,” New J. Phys. 23, 013004 (2021).9. H. Salih, J. R. Hance, W. McCutcheon, T. Rudolph, and J. Rarity, “Deterministic teleportation and universalcomputation without particle exchange,” arXiv preprint arXiv:2009.05564 (2020).10. A. C. Elitzur and L. Vaidman, “Quantum mechanical interaction-free measurements,” Foundations Phys.23, 987–997 (1993).11. Y. Zhang, A. Sit, F. Bouchard, H. Larocque, F. Grenapin, E. Cohen, A. C. Elitzur, J. L. Harden, R. W. Boyd,and E. Karimi, “Interaction-free ghost-imaging of structured objects,” Opt. Express 27, 2212–2224 (2019).12. J. R. Hance, J. Ladyman, and J. Rarity, “How quantum is quantum counterfactual communication?” Foun-dations Phys. 51, 12 (2021).

Exchange-Free Ghost Imaging

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Exchange-Free Ghost Imaging

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