The phenomenon of quantum interrogation allows one to optically detect the presence of an absorbing object, without the measuring light interacting with it. In an application of the quantum Zeno effect, the object inhibits the otherwise coherent evolution of the light, such that the probability that an interrogating photon is absorbed can in principle be arbitrarily small. We have implemented this technique, demonstrating efficiencies exceeding the 50% theoretical-maximum of the original "interaction-free" measurement proposal. We have also predicted and experimentally verified a previously unsuspected dependence on loss; efficiencies of up to 73% were observed and the feasibility of efficiencies up to 85% was demonstrated. (EV) showed that the wave-particle duality of light could allow "interaction-free" quantum interrogation of classical objects, in which the presence of a non-transmitting object is ascertained seemingly without interacting with it [3], i.e., with no photon absorbed or scattered by the object. In the basic EV technique, an interferometer is aligned to give complete destructive interference in one output port -the "dark" output -in the absence of an object. The presence of an opaque object in one arm of the interferometer eliminates the possibility of interference so that a photon may now be detected in this output. If the object is completely non-transmitting, any photon detected in the dark output port must have come from the path not containing the object. Hence, the measurements were deemed "interaction-free", though we stress that this term is sensible only for objects that completely block the beam. For measurements on partially-transmitting (and quantum) objects, we suggest the more general terminology "quantum interrogation". In any event there is necessarily a coupling between light and object (formally describable by some interaction Hamiltonian) -somewhat paradoxically, in the high-efficiency schemes discussed below, it is crucial that the possibility of an interaction exist, in order to reduce the probability that such an interaction actually occurs.The EV gedanken experiment has been realized using true single-photon states [4] and with a classical light beam attenuated to the single-photon level [5], as well as in neutron interferometry [6]. This methodology has even been employed to investigate the possibility of performing "absorption-free" imaging [7]. The EV technique suffers two serious drawbacks, however. First, the measurement result is ambiguous at least half of the timea photon may be detected in the non-dark output port whether or not there is an object. Second, at most half of the measurements are interaction-free [4,7]. Following Elitzur and Vaidman [3], we define a figure of merit η = P(QI)/[P(QI) + P(abs)] to characterize the "efficiency" of a given scheme, where P(QI) is the probability that the photon is detected in the otherwise dark port, and P(abs) is the probability that the object absorbs or scatters the photon. Physically, η is the fraction of measurements...
Using the complementary wave-and particle-like natures of photons, it is possible to make "interaction-free" measurements where the presence of an object can be determined with no photons being absorbed. We investigated several "interaction-free" imaging systems, i.e. systems that allow optical imaging of photosensitive objects with less than the classically expected amount of light being absorbed or scattered by the object. With the most promising system, we obtained high-resolution (10 µm), one-dimensional profiles of a variety of objects (human hair, glass and metal wires, cloth fibers), by raster scanning each object through the system. We discuss possible applications and the present and future limits for interaction-free imaging.PACS number(s): 03.65.Bz, 42.25.Hz
Defects in the XPD gene can result in several clinical phenotypes, including xeroderma pigmentosum (XP), trichothiodystrophy, and, less frequently, the combined phenotype of XP and Cockayne syndrome (XP-D/CS). We previously showed that in cells from two XP-D/CS patients, breaks were introduced into cellular DNA on exposure to UV damage, but these breaks were not at the sites of the damage. In the present work, we show that three further XP-D/CS patients show the same peculiar breakage phenomenon. We show that these breaks can be visualized inside the cells by immunofluorescence using antibodies to either ␥-H2AX or poly-ADP-ribose and that they can be generated by the introduction of plasmids harboring methylation or oxidative damage as well as by UV photoproducts. Inhibition of RNA polymerase II transcription by four different inhibitors dramatically reduced the number of UV-induced breaks. Furthermore, the breaks were dependent on the nucleotide excision repair (NER) machinery. These data are consistent with our hypothesis that the NER machinery introduces the breaks at sites of transcription initiation. During transcription in UV-irradiated XP-D/CS cells, phosphorylation of the carboxy-terminal domain of RNA polymerase II occurred normally, but the elongating form of the polymerase remained blocked at lesions and was eventually degraded.Xeroderma pigmentosum (XP), trichothiodystrophy (TTD), and Cockayne syndrome (CS) are genetic disorders, all associated with defects in nucleotide excision repair (NER) of DNA damage. Defects in XP have been assigned to eight complementation groups (XP-A through -G and variant) corresponding to proteins involved in different stages of the NER process. The XP-D complementation group is of particular interest and complexity, because mutations in the XPD gene can result in any of at least five different clinical phenotypes (23). XP and TTD are relatively frequent outcomes of XPD mutations, whereas the combined features of XP and CS, XP and TTD, or cranio-oculofacial-skeletal syndrome are rare outcomes (7,16,23). XPD protein is a subunit of transcription factor TFIIH, which is a multifunctional protein required for NER, basal transcription by RNA polymerase I (17) and II (10), and transcriptional activation (21, 27). It is likely that the complexity of the clinical outcomes arises because different mutations affect these various functions differentially. Thus, XP is thought to result if the mutation affects NER but has little effect on transcription. Conversely, TTD is thought to be the result of transcriptional deficiencies. In support of this hypothesis, each mutation site is specific for a particular disorder (37). Thus, for example, many XP patients with the XP clinical phenotype have a mutation at Arg683, whereas no TTD patients have this mutation. Conversely R112H and R722W are mutations found in several TTD patients but not in any XP patients (23). Furthermore, a mouse generated with the R722W mutation had many of the features of TTD (11).At the start of this study, only two...
The essential operations of a quantum computer can be accomplished using solely optical elements, with different polarization or spatial modes representing the individual qubits. We present a simple all-optical implementation of Grover's algorithm for efficient searching, in which a database of four elements is searched with a single query. By 'compiling' the actual setup, we have reduced the required number of optical elements from 24 to only 12. We discuss the extension to larger databases, and the limitations of these techniques.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.