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We report on an ion implantation technique utilizing a screening mask made of SiO$_2$ to control both the depth profile and the dose. By appropriately selecting the thickness of the screening layer, this method fully suppresses the ion channeling, brings the location of the highest NV density to the surface, and effectively reduces the dose by more than three orders of magnitude. With a standard ion implantation system operating at the energy of 10 keV and the dose of 10$^{11}$ cm$^2$ and without an additional etching process, we create single NV centers close to the surface with coherence times of a few tens of $\mu$s., Comment: 5 pages, 4 figures

We perform pulsed optically detected electron spin resonance to measure the DC magnetic field sensitivity and electronic spin coherence time T_2 of an ensemble of near-surface, high-density nitrogen-vacancy (NV) centers engineered to have a narrow magnetic resonance linewidth. Combining pulsed spectroscopy with dynamic nuclear polarization, we obtain the photon-shot-noise-limited DC magnetic sensitivity of 35 nT Hz^{-0.5}. We find that T_2 is controlled by instantaneous diffusion, enabling decoherence spectroscopy on residual nitrogen impurity spins in the diamond lattice and a quantitative determination of their density. The demonstrated high DC magnetic sensitivity and decoherence spectroscopy are expected to broaden the application range for two-dimensional magnetic imaging.

The effects of host isotope mass on the hyperfine interaction of group-V donors in silicon are revealed by pulsed electron nuclear double resonance (ENDOR) spectroscopy of isotopically engineered Si single crystals. Each of the hyperfine-split P-31, As-75, Sb-121, Sb-123, and Bi-209 ENDOR lines splits further into multiple components, whose relative intensities accurately match the statistical likelihood of the nine possible average Si masses in the four nearest-neighbor sites due to random occupation by the three stable isotopes Si-28, Si-29, and Si-30. Further investigation with P-31 donors shows that the resolved ENDOR components shift linearly with the bulk-averaged Si mass., 5 pages, 4 figures, 1 table

We have confirmed band warping effect of twodimensional holes confined at GaAs/AlGaAs singleheterojunction through classical commensurability resistance oscillations in anti-dot lattices (ADLs). The oscillations in the triangular ADLs are decomposed into three peaks, two of which are assigned to localized orbits of holes with a lighter effective math (l-hole), and the other is assigned to that of holes with heavier average effective math (h-hole). The latter assignment is possible only when the h-hole band is heavily warped, thus evidencing the warping. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We study the low-field magnetotransport of a twodimensional hole antidot lattice subject to strong spinorbit interaction. The Aharonov-Bohm type oscillations appearing in the low-temperature magnetoresistance have components corresponding to h /e and h /2e. We interpret the nodes seen in the h /e oscillations as signatures of the spin-orbit Berry phase, based on a simple simulation taking into account its contribution. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report the control of the orbital occupation by using the intra-orbital Coulomb interaction in quantum dots Tcoupled to quantum wires. With the change of the confinement potential, intra-orbital Coulomb interaction exceeds orbital level spacing and influences the orbital occupation. We realize such potential modification by changing either the gate design or the voltages applied to the gates. The rearrangement of the orbital occupation is confirmed from the response of the addition energy spectroscopy to the magnetic field. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present experiments on electronic states in few-electron lateral quantum dots side-coupled to quantum wires. The side-coupled structure enabled us to prepare the dots with various spatial sizes. The Coulomb energy and the quantum confinement energy depend on the dot size in different ways and thus the change in the size causes the change in the relative amplitude of the two energy scales. This results in non-monotonic occupation of single-electron energy levels. We have observed such non-trivial occupation through the collapse of the magic numbers and the response to magnetic field.

Purpose: To assess an accuracy of fiducial maker-based setup using ExacTrac (ExT-based setup) as compared with soft tissue-based setup using Cone-beam CT (CBCT-based setup) for patients with prostate cancer receiving intensity-modulated radiation therapy (IMRT) for the purpose of investigating whether ExT-based setup can be an alternative to CBCT-based setup. Methods: The setup accuracy was analyzed prospectively for 7 prostate cancer patients with implanted three fiducial markers received IMRT. All patients were treated after CBCT-based setup was performed and corresponding shifts were recorded. ExacTrac images were obtained before and after CBCT-based setup. The fiducial marker-based shifts were calculated based on those two images and recorded on the assumption that the setup correction was carried out by fiducial marker-based auto correction. Mean and standard deviation of absolute differences and the correlation between CBCT and ExT shifts were estimated. Results: A total of 178 image dataset were analyzed. On the differences between CBCT and ExT shifts, 133 (75%) of 178 image dataset resulted in smaller differences than 3 mm in all dimensions. Mean differences in the anterior-posterior (AP), superior-inferior (SI), and left-right (LR) dimensions were 1.8 ± 1.9 mm, 0.7 ± 1.9 mm, and 0.6 ± 0.8 mm, respectively. The percentages of shiftmore » agreements within ±3 mm were 76% for AP, 90% for SI, and 100% for LR. The Pearson coefficient of correlation for CBCT and ExT shifts were 0.80 for AP, 0.80 for SI, and 0.65 for LR. Conclusion: This work showed that the accuracy of ExT-based setup was correlated with that of CBCT-based setup, implying that ExT-based setup has a potential ability to be an alternative to CBCT-based setup. The further work is to specify the conditions that ExT-based setup can provide the accuracy comparable to CBCT-based setup.« less

Semiconductor quantum dots can be utilized to capture single electron or hole spins and they have therewith promise for various applications in fields like spintronics, spin based quantum information processing and chiral photonics. We integrate quantum dots into semiconductor microcavities to enhance light-matter interaction for ultrafast optical manipulation and read-out. Single electron and single hole spins can be statistically or deterministically loaded into the quantum dots and coherently controlled. Within the about μs-coherence times of the spins about 105 complete single qubit rotations can be performed with ultrafast optical pulses. By utilizing a Λ-type energy level system of a single quantum-dot electron spin in a magnetic field and ultrafast non-linear frequency conversion, quantum-dot spin-photon entanglement is observed.

The aim of our study was to analyze changes over time in the characteristics, treatment, and outcome of patients with primary central nervous system lymphoma (PCNSL). Data on 315 patients with histologically proven PCNSL undergoing radiotherapy between 2005 and 2009 were collected from 20 Japanese institutions using a questionnaire. These data were then compared with data on 273 patients treated during the period 1995–2004 and those on 466 patients treated during the period 1985–1994. In terms of patient and tumor characteristics, we found a significant increase in mean patient age in the 2005–2009 period compared to the 1985–2004 period (63 vs. 58–59 years, respectively) and in the percentage of patients with better performance status (PS) during the 2005–2009 period compared with the 1995–2004 period (World Health Organization PS 0–2: 73 vs. 65 %, respectively). Regarding treatment, relative to the 1995–2004 period, significant changes in the 2005–2009 period were (1) decreased rate of attempting tumor resection (23 vs. 44 %); (2) increased use of chemotherapy (78 vs. 68 %), and (3) increased use of methotrexate (MTX)-containing regimens (84 vs. 53 %). The 5-year overall survival rates were 15.3, 30.1, and 36.5 % for patients seen during the 1985–1994, 1995–2004, and 2005–2009 periods, respectively, but relapse-free survival did not improve between the 1995–2004 and 2005–2009 periods (26.7 vs. 25.7 % at 5 years, respectively). Patients receiving MTX-containing chemotherapy had 5-year survival rates of 19, 50, and 44 % during these three periods, respectively. Although patient backgrounds differed among the study periods, recent trends were a high patient age, better PS, avoidance of extensive tumor resection, more frequent use of chemotherapy, and improved survival. The recent improvement in survival may be due to improvements in second-line treatment and supportive care.

Entanglement between stationary quantum memories and photonic qubits is crucial for future quantum communication networks. Although high-fidelity spin-photon entanglement was demonstrated in well-isolated atomic and ionic systems, in the solid-state, where massively parallel, scalable networks are most realistically conceivable, entanglement fidelities are typically limited due to intrinsic environmental interactions. Distilling high-fidelity entangled pairs from lower-fidelity precursors can act as a remedy, but the required overhead scales unfavourably with the initial entanglement fidelity. With spin-photon entanglement as a crucial building block for entangling quantum network nodes, obtaining high-fidelity entangled pairs becomes imperative for practical realization of such networks. Here we report the first results of complete state tomography of a solid-state spin-photon-polarization-entangled qubit pair, using a single electron-charged indium arsenide quantum dot. We demonstrate record-high fidelity in the solid-state of well over 90%, and the first (99.9%-confidence) achievement of a fidelity that will unambiguously allow for entanglement distribution in solid-state quantum repeater networks.

The radiation oncology seminar for medical students and residents was initiated by the Japanese Society for Therapeutic Radiology and Oncology (JASTRO) with the aim of increasing the numbers of radiation oncologists. We investigated the long-term results related to the career paths of the program participants. This study enrolled 531 individuals who were medical students and residents at the time of program participation, between 1995 and 2011. We surveyed participants with regard to their affiliation status with the Japan Radiological Society (JRS) and JASTRO and whether they were board-certified radiation oncologists. Forty-two percent of the participants were members of JRS and 26.4 % were members of JASTRO. The membership status with JASTRO was investigated in program participants from 2004 to 2009, and comparison by status revealed that 30.1 % of medical students and 47.2 % of residents were members, with a significant difference (p = 0.013). As high as 92.3 % of the participants in the 1995–2001 cohort who had joined JRS and JASTRO were board-certified radiation oncologists. This program has greatly contributed to increasing the numbers of radiation oncologists. Because residents had a higher rate of affiliation than medical students, it is necessary to share information with not only medical universities, but also teaching hospitals.

Individual electron and hole quantum dot spin qubits can be coherently manipulated using picosecond modelocked laser pulses; an all-optical spin-echo was implemented that decouples slow environmental changes. While dephasing and decoherence mechanisms for electrons and holes are intrinsically different, similar qualitative results are obtained, except for dynamic nuclear polarization effects that affect the controllability of electrons. In addition, we demonstrate spin-photon entanglement in a charged InAs quantum dot, using an ultrafast downconversion technique that converts a single, spontaneously emitted photon at 900 nm into a 1560 nm photon with picosecond timing resolution. This ultrafast conversion technique allows quantum erasure of which-path frequency information in the spontaneous emission process.

Purpose: To establish a simple relation of backscatter dose enhancement around a high-Z dental alloy in head and neck radiation therapy to its average atomic number based on Monte Carlo calculations. Methods: The PHITS Monte Carlo code was used to calculate dose enhancement, which is quantified by the backscatter dose factor (BSDF). The accuracy of the beam modeling with PHITS was verified by comparing with basic measured data namely PDDs and dose profiles. In the simulation, a high-Z alloy of 1 cm cube was embedded into a tough water phantom irradiated by a 6-MV (nominal) X-ray beam of 10 cm × 10 cm field size of Novalis TX (Brainlab). The ten different materials of high-Z alloys (Al, Ti, Cu, Ag, Au-Pd-Ag, I, Ba, W, Au, Pb) were considered. The accuracy of calculated BSDF was verified by comparing with measured data by Gafchromic EBT3 films placed at from 0 to 10 mm away from a high-Z alloy (Au-Pd-Ag). We derived an approximate equation to determine the relation of BSDF and range of backscatter to average atomic number of high-Z alloy. Results: The calculated BSDF showed excellent agreement with measured one by Gafchromic EBT3 films at from 0 to 10 mm away from the high-Z alloy. We found the simple linear relation of BSDF and range of backscatter to average atomic number of dental alloys. The latter relation was proven by the fact that energy spectrum of backscatter electrons strongly depend on average atomic number. Conclusion: We found a simple relation of backscatter dose enhancement around high-Z alloys to its average atomic number based on Monte Carlo calculations. This work provides a simple and useful method to estimate backscatter dose enhancement from dental alloys and corresponding optimal thickness of dental spacer to prevent mucositis effectively.

There is no standard therapy for elderly patients with high-grade glioma. We have adopted short course radiotherapy for such patients since 2005. The efficacy of this therapy was assessed retrospectively.This study reviewed 16 newly diagnosed high-grade glioma patients aged 75 years or older who were treated with short course radiotherapy (focal radiation in daily fraction of 3 Gy given 5 days per week, for a total dose of 39 Gy).All patients received 100% of the planed radiation dose. No patients received prior or concomitant chemotherapy. Thirteen patients had died and median follow-up period was 9 months at the time of analysis. The median age at surgery was 79 years (range 75-86). The estimated median overall survival was 9.6 months. The median Karnofsky Performance Status on admission was 60% (range 40-90) and at discharge was 60% (range 40-80). The median length of hospital stay was 38 days (range 19-61). There is no severe adverse events related to radiation therapy. The rate of discharge to home was 69%.Short course radiotherapy can reduce the treatment time and adverse events of conventional radiotherapy without decrement in survival. This therapy seems to be a considerable treatment option for elderly patients with high-grade glioma.

The goals of treatment for brain metastases (BMs) include preservation of function and improvement of survival. Although whole brain radiotherapy (WBRT) has been a mainstay in the treatment of BMs, stereotactic radiosurgery (SRS) monotherapy has been increasingly used because of concern about the deterioration of neurocognitive function as a late adverse effect of WBRT. The results of four randomized controlled trials comparing focal treatment alone versus focal treatment combined with WBRT have shown, however, that SRS monotherapy significantly increases the risk of brain tumor recurrence (BTR) and that this increased risk of BTR may cause deterioration of neurocognitive function. We suggest identifying patients according to their risk of BTR when selecting treatment. Patients who have solitary BM with the absence of extracranial metastases may be indicated for SRS monotherapy given the lower risk of BTR compared with those having multiple BMs or extracranial metastases.

We report electron paramagnetic resonance EPR experiments of phosphorus donors in isotopically controlled silicon single crystals. By varying the concentration of the 29 Si isotope, f, from 0.075% to 99.2%, we systematically study the effect of the environmental nuclear spins on the donor-electron spin. We find excellent agreement between experiment and theory for decoherence times due to nuclear-induced spectral diffusion, clarifying that the nuclear-induced decoherence is dominant in the range of f studied. We also observe that the EPR linewidth shows a transition from the square-root dependence to the linear dependence on f, in agreement with theoretical predictions.

We demonstrate a new method for locally probing the edge states in the quantum Hall regime utilizing a side coupled quantum dot positioned at an edge of a Hall bar. By measuring the tunneling of electrons from the edge states into the dot, we acquire information on the local electrochemical potential and electron temperature of the edge states. Furthermore, this method allows us to observe the spatial modulation of the electrostatic potential at the edge state due to many-body screening effect., Comment: 5 pages, 5 figures

We propose realistic methods to detect local spin polarization, which utilize a quantum dot side coupled to the target system. By choosing appropriate states in the dot, we can put spin selectivity to the dot and detect spins in the target with small disturbance. We also present an experiment which realizes one of the proposed spin detection schemes in magnetic fields., Comment: 5 pages, 6 figures

We report observation of spin-orbit Berry's phase in the Aharonov-Bohm (AB) type oscillation of weak field magnetoresistance in an anti-dot lattice (ADL) of a two-dimensional hole system. An AB-type oscillation is superposed on the commensurability peak, and the main peak in the Fourier transform is clearly split up due to variation in Berry's phase originating from the spin-orbit interaction. A simulation considering Berry's phase and the phase arising from the spin-orbit shift in the momentum space shows qualitative agreement with the experiment., Comment: 13 pages, 5 figures

We have studied the Fano effect in a few-electron quantum dot side-coupled to a quantum wire. The conductance of the wire, which shows an ordinal staircase-like quantization without the dot, is modified through the interference (the Fano effect) and the charging effects. These effects are utilized to verify the exhaustion of electrons in the dot. The "addition energy spectrum" of the dot shows a shell structure, indicating that the electron confinement potential is fairly circular. A rapid sign inversion of the Fano parameter on the first conductance plateau with the change of the wire gate voltage has been observed, and explained by introducing a finite width of dot-wire coupling., 11 pages, 7 figures

Pharaonis phoborhodopsin (ppR), also called pharaonis sensory rhodopsin II, NpSRII, is a photoreceptor for the photophobic response of Natronomonas pharaonis. Tryptophan 182 (W182) of bacteriorhodopsin (bR) is near the chromophore retinal and has been suggested to interact with retinal during the photoreaction and also to be involved in the hydrogen-bonding network around the retinal. W182 of bR is conserved in ppR as tryptophan 171 (W171). To elucidate whether W171 of ppR interacts with retinal during the photoreaction and/or is involved in the hydrogen-bonding network as in bR, we formed W171-substituted mutants of ppR, W171A and W171T. Our low-temperature spectroscopic study has revealed that the substitution of W171 to Ala or Thr resulted in the stabilization of M- and O-intermediates. The stability of M and absorption spectral changes during the M-decay were different depending on the substituted residue. These findings suggest that W171 in ppR interacts with retinal and the degree of the interaction depends on the substituted residues, which might be rate determining in the M-decay. In addition, the involvement of W171 in the hydrogen-bonding network is suggested by the O-decay. We also found that glycerol slowed the decay of M and not of O.

To evaluate the incidence and risk factors of enlargement of cardiac silhouette on chest radiographs after radiotherapy for esophageal cancer. We analyzed 67 patients with esophageal cancer who received external beam radiation therapy with a total dose of ≥50 Gy and were followed for ≥6 months. Sixteen patients received radiation alone, and the remaining 51 received chemoradiotherapy. The difference between the cardiothoracic ratio (CTR) on the pretreatment chest radiograph and that on the posttreatment radiograph with maximum cardiac silhouette for each patient was used for the analysis. The average maximum increase in CTR for the entire group was 4.5%, which was statistically significant. Only the area of the cardiac silhouette in the initial radiation field was a significant risk factor for enlargement of the cardiac silhouette. Pericardial effusions were observed in all patients who underwent computed tomography with severe enlargement of the cardiac silhouette. The CTR value significantly increased after radiotherapy for esophageal cancer. Radiation-induced pericardial effusion may be the main cause of enlargement of the cardiac silhouette. The irradiated cardiac area was the only significant risk factor for enlargement of the cardiac silhouette; the use of chemotherapy was not.

We report NMR experiments using high-power rf decoupling techniques to show that a $^{29}\mathrm{Si}$ nuclear spin in a solid silicon crystal at room temperature can preserve quantum phase for ${10}^{9}$ precessional periods. The coherence times we report are more than four orders of magnitude longer than for any other observed solid-state qubit. We also examine coherence times using magic-angle-spinning techniques and in isotopically altered samples. In high-quality crystals, coherence times are limited by residual dipolar couplings and can be further improved by isotopic depletion. In defect-heavy samples, we provide evidence for decoherence limited by a noise process unrelated to the dipolar coupling. The nonexponential character of these data is compared to a theoretical model for decoherence due to the same charge trapping mechanisms responsible for $1∕f$ noise. These results provide insight into proposals for solid-state nuclear-spin-based quantum memories and quantum computers based on silicon.

We report a pulsed EPR study of the phase relaxation of electron spins bound to phosphorus donors in isotopically purified 29^Si and natural abundance Si single crystals measured at 8 K., 5 pages, 3 figures

A solid-state implementation of a quantum computer composed entirely of silicon is proposed. Qubits are Si-29 nuclear spins arranged as chains in a Si-28 (spin-0) matrix with Larmor frequencies separated by a large magnetic field gradient. No impurity dopants or electrical contacts are needed. Initialization is accomplished by optical pumping, algorithmic cooling, and pseudo-pure state techniques. Magnetic resonance force microscopy is used for readout. This proposal takes advantage of many of the successful aspects of solution NMR quantum computation, including ensemble measurement, RF control, and long decoherence times, but it allows for more qubits and improved initialization., ReVTeX 4, 5 pages, 2 figures

The linewidth of the low-field electrically detected magnetic resonance (LFEDMR) of phosphorus electrons in silicon is investigated using samples with various 29Si nuclear spin fractions and is compared to that of X-band electron paramagnetic resonance (EPR). The linewidths of LFEDMR and EPR are the same even though LFEDMR signals are obtained based on spin-dependent recombination, suggesting that the interaction between electron spins of phosphorus and recombination centers is strong enough for the LFEDMR detection but weak enough not to affect the linewidths. This favorable balance makes LFEDMR an attractive method to elucidate the low-field behavior of paramagnetic defects in semiconductors.

We report excited-state spectroscopy on a quantum dot side-coupled to a quantum wire with accurate energy estimation. Our method utilizes periodic voltage pulses on the dot, and the energy calibration is performed with reference to the bias voltage across the wire. We demonstrate the observation of the orbital excited state and the Zeeman splitting in a single dot., 3 pages, 4 figures

We study charge states of a superconducting single-electron transistor (SSET) fabricated on a heterostructure substrate that can be switched from insulating to conductive. We probe the charge states by microwave irradiation and subsequent observation of photon-assisted Josephson quasiparticle current, which allow us to obtain the energy dispersion relation in the quasicharge space. When the substrate is insulating, the charge states show an energy-dispersion curve with a gap, manifesting that coherent superposition of the two charge states is realized. When the substrate becomes conductive, its two-dimensional electrons capacitively couple to the SSET and modify the degree of dissipation to its electromagnetic environment. The dispersion relation then becomes linear, and its slope agrees with the value estimated from the charging energy including the capacitance of the two-dimensional electrons. This indicates that quantum coherence between the two charge states is lost due to the coupling with the environment.

We report an ultrafast downconversion quantum interface, where 910-nm single photons from a quantum dot are downconverted to the 1.5-μm telecom band with sub-10 picosecond pulses at 2.2-μm, enabling the demonstration of quantum-dot spin-photon entanglement.

The aim of this study was to investigate the impact of multileaf collimator width (MLC‐W) on intraprostatic dose painting plans for prostate cancer. Prostate cancer maps based on the histopathological findings were superimposed onto simulation CT images. Clinical target volume (CTV) 1 was defined as the prostate and the base of the seminal vesicles, and CTV2 was defined as the dominant intraprostatic lesions. Planning target volume (PTV) 1 and PTV2 were delineated by adding 5 mm margins to CTV1 and CTV2, respectively. For each case, two dose painting plans were created to deliver 74 Gy to PTV1 and 84 Gy to PTV2 with dynamic multileaf collimator technique using two different MLCs: m3 (MLC‐W: 3 mm) and Millennium (5 mm). Plans were evaluated by comparing the conformation number (CN), a quantity that defines the degree of conformality. The CNs for plans using the m3 and Millennium were 0.68 and 0.67 for PTV1 and 0.59 and 0.58 for PTV2, respectively. The CNs tended to be higher for a thinner leaf width (p

We report background-free, near-infrared-to-telecom quantum frequency down-conversion, mediating two-photon interference with a mean wavepacket overlap larger than 0.89, regardless of the original separation between photon sources in wavelength (900- and 911-nm), wavepacket, and distance (2 km).