Tomohisa Nagata
Hokkaido University
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Tomohisa Nagata.
Science | 2007
Tomohisa Nagata; Ryo Okamoto; Jeremy L. O'Brien; Keiji Sasaki; Shigeki Takeuchi
Precision measurements are important across all fields of science. In particular, optical phase measurements can be used to measure distance, position, displacement, acceleration, and optical path length. Quantum entanglement enables higher precision than would otherwise be possible. We demonstrated an optical phase measurement with an entangled four-photon interference visibility greater than the threshold to beat the standard quantum limit—the limit attainable without entanglement. These results open the way for new high-precision measurement applications.
Science | 2009
Ryo Okamoto; Jeremy L. O'Brien; Holger F. Hofmann; Tomohisa Nagata; Keiji Sasaki; Shigeki Takeuchi
The ability to filter quantum states is a key capability in quantum information science and technology, in which one-qubit filters, or polarizers, have found wide application. Filtering on the basis of entanglement requires extension to multi-qubit filters with qubit-qubit interactions. We demonstrated an optical entanglement filter that passes a pair of photons if they have the desired correlations of their polarization. Such devices have many important applications to quantum technologies.
New Journal of Physics | 2008
Ryo Okamoto; Holger F. Hofmann; Tomohisa Nagata; Jeremy L. O'Brien; Keiji Sasaki; Shigeki Takeuchi
Quantum metrology promises greater sensitivity for optical phase measurements than could ever be achieved classically. Here, we present a theory of the phase sensitivity for the general case where the detection probability is given by an N photon interference fringe. We find that the phase sensitivity has a complicated dependence on both the intrinsic efficiency of detection and the interference fringe visibility V. Most importantly, the phase that gives maximum phase sensitivity is in general not the same as the phase at which the slope of the interference fringe is a maximum, as has previously been assumed. We determine the parameter range where quantum enhanced sensitivity can be achieved. In order to illustrate these theoretical results, we perform a four-photon experiment with = 3/4 and V = 82±6% (an extension of our previous work (Nagata et al 2007 Science 316 726)) and find a phase sensitivity 1.3 times greater than the standard quantum limit at a phase different to that which gives maximum slope of the interference fringe.
Journal of The Optical Society of America B-optical Physics | 2010
Pruet Kalasuwan; Gabriel Mendoza; Anthony Laing; Tomohisa Nagata; Jack Coggins; Mark Callaway; Shigeki Takeuchi; André Stefanov; Jeremy L. O'Brien
We show how an entangled cluster state encoded in the polarization of single photons can be straightforwardly expanded by deterministically entangling additional qubits encoded in the path degree of freedom of the constituent photons. This can be achieved using a polarization–path controlled-phase gate. We experimentally demonstrate a practical and stable realization of this approach by using a Sagnac interferometer to entangle a path qubit and polarization qubit on a single photon. We demonstrate precise control over phase of the path qubit to change the measurement basis and experimentally demonstrate properties of measurement-based quantum computing using a two-photon, three-qubit cluster state.
Proceedings of SPIE | 2014
Richard Stahl; Geert Vanmeerbeeck; Gauthier Lafruit; Roeland Huys; Veerle Reumers; Andy Lambrechts; Chao-Kang Liao; Chin-Chun Hsiao; Masayuki Yashiro; Masashi Takemoto; Tomohisa Nagata; Shinichi Gomi; Kunitada Hatabayashi; Yasuhiro Oshima; Shigenori Ozaki; Naoki Nishishita; Shin Kawamata
Lens-free inline Holographic Microscopy (LHM) holds great promise for biomedical and industrial applications thanks to its conceptual simplicity. However, the challenge lies in achieving an image quality comparable to conventional microscopes. We demonstrate a high-throughput LHM system that is able to resolve 1.23μm-thin lines on a standard USAF 1951 test target with 1.67μm pixels at the full field-of-view (>29mm2). The system is based on a unique multiwavelength iterative-phase-retrieval method, using customized hardware and real-time post-processing software. We have evaluated our system in experiments ranging from single-cell inspection to in-vitro imaging of stem-cell colonies.
New Journal of Physics | 2010
Tomohisa Nagata; Ryo Okamoto; Holger F. Hofmann; Shigeki Takeuchi
Possible error sources in an experimentally realized linear-optics controlled-Z gate (Okamoto et al 2005 Phys. Rev. Lett. 95 210506) are analyzed by considering the deviations of the beam splitting ratios from the ideal values (δRH, δRV), the polarization-dependent phase shift (birefringence) of the optical components (δ) and the mode mismatch of input photons (δξ). It is found that the error rate is linearly dependent on δRV and δξ, while the dependence on δRH and δ is approximately quadratic. As a practical result, the gate is much more sensitive to small errors in RV than in RH. Specifically, the reflectivity error for vertical polarization must be less than 0.1% to realize a gate with an error of less than 0.1%, whereas the reflectivity error for horizontal polarization can be up to 1%. It is also shown that the effects of different error sources are not independent of each other (linear error model). Under certain conditions, the deviation from the linear error model exceeds 10% of the total error. The method of analysis used illustrates the basic features of errors in general linear optics quantum gates and circuits, and can easily be adapted to any other device of this type.
Proceedings of SPIE | 2010
Tomohisa Nagata; Ryo Okamoto; Masato Tanida; Holger F. Hofmann; Shigeki Takeuchi
Possible error sources in an experimentally realized linear-optics controlled-Z gate[1] are analyzed by considering the deviations of the beam splitting ratios from the ideal values (δRH,δRV), the polarization-dependent phase shift (birefringence) of the optical components (δφ) and the mode mismatch of input photons (δξ). It is found that the error rate is linearly dependent on δRV and δξ , while the dependence on δRH and δφ is approximately quadratic. As a practical result, the gate is much more sensitive to small errors in RV than in RH. Specifically, the reflectivity error for vertical polarization must be less than 0.1% to realize a gate with an error of less than 0.1%, whereas the reflectivity error for horizontal polarization can be up to 1%. It is also shown that the effects of different error sources are not independent of each other (linear error model). Under certain conditions, the deviation from the linear error model exceeds 10% of the total error. The method of analysis used illustrates the basic features of errors in general linear optics quantum gates and circuits, and can easily be adapted to any other device of this type.
european quantum electronics conference | 2009
Ryo Okamoto; Jeremy L. O'Brien; Holger F. Hofmann; Tomohisa Nagata; Keiji Sasaki; Shigeki Takeuchi
The ability to filter quantum states is a key capability in quantum information science and technology, where one-qubit filters, or polarizers, have found wide application. Filtering on the basis of entanglement requires extension to multi-qubit filters with qubit-qubit interactions. Such devices have many important applications to quantum technologies.
Proceedings of SPIE | 2009
Tomohisa Nagata; Ryo Okamoto; Keiji Sasaki; Shigeki Takeuchi
The errors in linear optics controlled not (C-NOT) gates are analyzed considering the polarization-dependent phase sifts, in addition to the incorrectness of the beam splitting ratios. It is shown that the phase sifts at the optical components is as crucial as other error sources discussed in the previous studies. Such a phase shift unintentionally changes the linearly-polarized photons into a elliptically polarized ones. The operators for a beam splitting device and the process matrix of the C-NOT operation including such errors are also given.
international quantum electronics conference | 2007
Tomohisa Nagata; Ryo Okamoto; Holger F. Hofmann; Shigeki Takeuchi; Keiji Sasaki
In our paper, we report the analysis of errors in the C-NOT gate using a high-precision test-bed. From the result of previous experiment, we have identified two main causes of errors: one is the mismatch between optical modes, and the other is the un-intentional phase shift between two polarization, horizontal polarizations and vertical polarization. To evaluate these factors more precisely, we construct a test-bed setup in which piezo-electric stages are used to avoid mode mismatch, and the extinction ratio of polarization is kept below 10-3. In the poster, we will report the experimental results with the test-bed and the analysis of errors in detail.