Generating a state tt-design by diagonal quantum circuits

We investigate protocols for generating a state $t$-design by using a fixed separable initial state and a diagonal-unitary $t$-design in the computational basis, which is a $t$-design of an ensemble of diagonal unitary matrices with random phases as their eigenvalues. We first show that a diagonal-unitary $t$-design generates a $O(1/2^N)$-approximate state $t$-design, where $N$ is the number of qubits. We then discuss a way of improving the degree of approximation by exploiting non-diagonal gates after applying a diagonal-unitary $t$-design. We also show that it is necessary and sufficient to use $O(\log_2 t)$-qubit gates with random phases to generate a diagonal-unitary $t$-design by diagonal quantum circuits, and that each multi-qubit diagonal gate can be replaced by a sequence of multi-qubit controlled-phase-type gates with discrete-valued random phases. Finally, we analyze the number of gates for implementing a diagonal-unitary $t$-design by {\it non-diagonal} two- and one-qubit gates. Our results provide a concrete application of diagonal quantum circuits in quantum informational tasks.Comment: ver. 1: 15 pages, 1 figures. ver.2: 16 pages, 2 figures, major changes, we corrected a mistake, which slightly changes a main conclusion, added a new result, and improved a presentation. ver.3: 11 pages, 2 figures, published versio

Black holes as clouded mirrors: the Hayden-Preskill protocol with symmetry

The Hayden-Preskill protocol is a quantum information theoretic model of the black hole information paradox. Based on the protocol, it was revealed that information scrambling and entanglement lead to an instant leakage of information. In this paper, we study the information paradox with symmetry in the framework of the Hayden-Preskill protocol. Symmetry is an important feature of black holes that induces yet more conceptual puzzles in the regime of quantum gravity. We especially consider an axial symmetry and clarify its consequences in the information leakage problem. Using a partial decoupling approach, we first show that symmetry induces a \emph{delay} of information leakage and an \emph{information remnant}, both of which can be macroscopically large for certain initial conditions. We then clarify the physics behind the delay and the information remnant. By introducing the concept of \emph{clipping of entanglement}, we show that the delay is characterized by thermodynamic properties of the black hole associated with the symmetry. We also show that the information remnant is closely related to the symmetry-breaking of the black hole. These relations indicate the existence of non-trivial microscopic-macroscopic correspondences in the information leakage problem.Comment: Ver.1: 7 pages + Supplementary. Ver.2: short version (14 pages) + long version (47 pages). Presentation improved. Connection to thermodynamics is much more elaborated. Ver.3: Substantial update of presentation and others, including the title. 21 pages + 6 pages of appendice

Quantum key distribution with an efficient countermeasure against correlated intensity fluctuations in optical pulses

Quantum key distribution (QKD) allows two distant parties to share secret keys with the proven security even in the presence of an eavesdropper with unbounded computational power. Recently, GHz-clock decoy QKD systems have been realized by employing ultrafast optical communication devices. However, security loopholes of high-speed systems have not been fully explored yet. Here we point out a security loophole at the transmitter of the GHz-clock QKD, which is a common problem in high-speed QKD systems using practical band-width limited devices. We experimentally observe the inter-pulse intensity correlation and modulation-pattern dependent intensity deviation in a practical high-speed QKD system. Such correlation violates the assumption of most security theories. We also provide its countermeasure which does not require significant changes of hardware and can generate keys secure over 100 km fiber transmission. Our countermeasure is simple, effective and applicable to wide range of high-speed QKD systems, and thus paves the way to realize ultrafast and security-certified commercial QKD systems

Survival in non-small cell lung cancer patients with versus without prior cancer

Clinical trials on cancer treatments frequently exclude patients with prior cancer, but more evidence is needed to understand their possible effects on outcomes. This study analyzed the prognostic impact of prior cancer in newly diagnosed non-small cell lung cancer (NSCLC) patients while accounting for various patient and cancer characteristics. Using population-based cancer registry data linked with administrative claims data, this retrospective cohort study examined patients aged 15–84 years diagnosed with NSCLC between 2010 and 2015 in Japan. Cox proportional hazards models were used to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs) of all-cause mortality in patients with versus without prior cancer. The analysis was stratified according to NSCLC stage and diagnostic time intervals between prior cancers and the index NSCLC. We analyzed 9103 patients (prior cancer: 1416 [15.6%]; no prior cancer: 7687 [84.4%]). Overall, prior cancer had a non-significant mortality HR of 1.07 (95% CI: 0.97–1.17). Furthermore, prior cancer had a significantly higher mortality hazard for diagnostic time intervals of 3 years (HR: 1.23, 95% CI: 1.06–1.43) and 5 years (1.18, 1.04–1.33), but not for longer intervals. However, prior cancer in patients with more advanced NSCLC did not show a higher mortality risk for any diagnostic time interval. Smoking-related prior cancers and prior cancers with poorer prognosis were associated with poorer survival. NSCLC patients with prior cancer do not have an invariably higher risk of mortality, and should be considered for inclusion in clinical trials depending on their cancer stage

Factors Affecting the Quality of Life of Patients with Painful Spinal Bone Metastases

This study examined changes in the quality of life (QOL), as well as the factors affecting QOL, among patients with painful spinal bone metastases without paralysis for 1 month after radiotherapy. Methods: This study included 79 participants (40 male and 39 female; median age, 65 (42-88) years) who had undergone radiotherapy for painful spinal bone metastases without paralysis. Patients' age, sex, activities of daily living (Barthel index), pain, spinal instability (spinal instability neoplastic score [SINS]), and QOL (EORTC QLQ-C30) were investigated. Results: Having an unstable SINS score was a positive factor for global health status (p < 0.05). The improvement in activities of daily living and response to pain were positive factors for physical function (p < 0.05). A positive effect on emotional function was confirmed among female patients (p < 0.05). Conclusion: Engaging in rehabilitation along with radiotherapy leads to improvements in QOL for patients with spinal bone metastases

Association between Overall Survival and Activities of Daily Living in Patients with Spinal Bone Metastases

Objective: This study aimed to investigate the association between overall survival (OS) and activities of daily living (ADL) in patients with skeletal-related events. In this study, 265 patients whose clinical parameters were available before radiotherapy were investigated. Methods: Age, sex, ADL, pain, the primary site, spinal level of bone metastases, spinal instability, treatment strategy, including chemotherapy or palliative treatment, and OS were investigated. ADL patients with a Barthel index of >= 90 were classified as the high ADL group, while those with a score = 160 days were classified as the non-poor prognosis group, and those who survived <160 days were classified as the poor prognosis group. Results: Age, sex, ADL, pain, the primary site, and treatment strategy for OS were different between the two groups (p < 0.1). Logistic regression analysis revealed that ADL, the primary site, and treatment strategy were significant predictors of OS (p < 0.05). High ADL, breast cancer, and chemotherapy had a positive effect on OS. Conclusions: It is suggested that improvements may be obtained by performing rehabilitation interventions to maintain and improve ADL, by constructing a system for monitoring spinal bone metastases with images before ADL decreases, and by performing interventions such as changes in treatment methods such as RT or surgery at appropriate times

Influence of and Risk Factors for Axillary Web Syndrome Following Surgery for Breast Cancer

In this study, we examined whether axillary web syndrome (AWS) in patients with breast cancer following axil-lary lymph node dissection affects range of motion (ROM), upper extremity function, and quality of life (QOL). The risk factors for AWS were also evaluated in a total of 238 consecutive breast cancer patients follow-ing axillary lymph node dissection. At 1, 2, and 3 months after surgery, there were no significant differences between the AWS group and the non-AWS group in upper-limb function or QOL. At 2 months after surgery, shoulder flexion and abduction ROM were significantly higher in the AWS group than in the non-AWS group (p < 0.05). Self-training time at home was not significantly different between the groups at 1, 2, or 3 months. Only age was a significant predictor of AWS at 1 month after surgery (p < 0.05). The AWS group in the present study did not have worse results for shoulder joint ROM, upper-limb function, and QOL than the non-AWS group. Younger age should be useful for predicting the development of AWS in the early postoperative period