Decoding quantum errors with the Gottesman-Kitaev-Preskill code

Implementing quantum error correction has been difficult in practice. Techniques from engineering, computer science, coding theory, experimental and theoretical physics have been blended together to tackle this problem. Traditionally, quantum error correcting codes mostly focus on dealing with phenomenological Pauli errors primarily due to their theoretical convenience. But this approach neglects physical types of noise, which are more realistically modelled with physically motivated noise models. This work focuses on a specific encoding in quantum computing called the Gottesman-Kitaev Preskill (GKP) codes. Firstly we study the basic properties and quantum estimation capabilities of a closely related state that is symmetric in phase space called the grid sensor state, motivating the GKP code as a good candidate for physical qubit level error correction in quantum optics. The grid codes aim to correct for errors before they build up to become Pauli errors. Then, we propose a quantum error correction protocol for continuous-variable finite-energy, approximate GKP states undergoing small Gaussian random displacement errors, based on the scheme of Glancy and Knill [Phys. Rev. A 73, 012325 (2006)]. We show that combining multiple rounds of error-syndrome extraction with Bayesian estimation offers enhanced protection of GKP-encoded qubits over comparible single-round approaches. Furthermore, we show that the expected total displacement error incurred in multiple rounds of error followed by syndrome extraction is bounded by 2√π. Finally, we show that by recompiling the syndrome-extraction circuits, all the squeezing operations can be subsumed into auxiliary state preparation, reducing them to beamsplitter transformations and quadrature measurements.Open Acces

Flexible entangled state generation in linear optics

Fault-tolerant quantum computation can be achieved by creating constant-sized, entangled resource states and performing entangling measurements on subsets of their qubits. Linear optical quantum computers can be designed based on this approach, even though entangling operations at the qubit level are non-deterministic in this platform. Probabilistic generation and measurement of entangled states must be pushed beyond the required threshold by some combination of scheme optimisation, introduction of redundancy and auxiliary state assistance. We report progress in each of these areas. We explore multi-qubit fusion measurements on dual-rail photonic qubits and their role in measurement-based resource state generation, showing that it is possible to boost the success probability of photonic GHZ state analysers with single photon auxiliary states. By incorporating generators of basic entangled "seed" states, we provide a method that simplifies the process of designing and optimising generators of complex, encoded resource states by establishing links to ZX diagrams.Comment: Comments welcom

Perceived Importance of Portfolios in a Smart CV after an Education Reform: An Empirical Analysis

Recent developments in recruitment processes have demonstrated that job applicants are increasingly using online Smart CVs instead of traditional approaches like hardcopy or emailing CVs. This study aims at examining perceived importance university undergraduate students of Hong Kong place or put on portfolios of Smart CVs, such as internship experience, exchange experience, scholarships & awards, participation in competitions, academic performance, and extra-curricular activities when building a Smart CV, and on investigating potential effects of the 3+3+4 academic reform in Hong Kong and admission mode. Participants were 256 undergraduate students in BBA majoring either in Information Management or in Electronic Commerce. A survey consisting of 44 items, which measured perceptions on the importance of the 6 proposed portfolios of Smart CVs, was used to collect data. Principal component analysis was used to analyze the items and 34 items were included in the final factor structure out of which 27 items got retained after subsequent reliability analysis. The 6 portfolios were positively inter-correlated. Students who were admitted under the new 4-year undergraduate curriculum using examination results of the new Hong Kong Diploma of Secondary Education (HKDSE) perceived internship experience and participation in competitions as more important in their Smart CVs, which was not the case with those who were admitted under the 3-year undergraduate curriculum using the results of the Hong Kong Advanced Level Examination (HKALE), which is no longer in use since 2012. The admission routes of students did not affect perceived importance in a Smart CV of the 6 proposed portfolios

Effects of risk assessment and management programme for hypertension on clinical outcomes and cardiovascular disease risks after 12 months: a population-based matched cohort study

Objectives: This study evaluated the effectiveness of a structured multidisciplinary risk assessment and management programme for patients with hypertension (RAMP-HT) who were managed in public primary care clinics but had suboptimal blood pressure (BP) control in improving BP, LDL-cholesterol (LDL-C) and predicted 10-year cardiovascular disease (CVD) risk after 12 months of intervention. Methods: A total of 10 262 hypertension patients with suboptimal BP despite treatment, aged less than 80 years and without existing CVD were enrolled in RAMP-HT between October 2011 and March 2012 from public general out-patient clinics in Hong Kong. Their clinical outcomes and predicted 10-year CVD risk were compared with a matched cohort of hypertension patients who were receiving usual care in general out-patient clinics without any RAMP-HT intervention by propensity score matching. Multivariable linear and logistic regressions were used to determine the independent effectiveness of RAMP-HT after adjusting for potential confounding variables. Results: Compared with the usual care group after 12 months, significantly greater proportions of RAMP-HT participants achieved target BP (i.e. BP 20%) (OR = 1.13, P < 0.01). RAMP-HT participants also had significantly greater reduction in predicted 10-year CVD risk by 0.44% (coefficient = -0.44, P < 0.01). Conclusion: The structured multidisciplinary RAMP-HT was more effective than usual care in achieving target BP, LDL-C and reducing predicted 10-year CVD risk in public primary care patients with suboptimal hypertension control after 12 months of intervention. A long-term follow-up should be conducted to confirm whether the improvement in clinical outcomes can be translated into actual reductions in CVD complications and mortalities and whether such approach is cost-effective.published_or_final_versio

High photon-loss threshold quantum computing using GHZ-state measurements

We propose fault-tolerant architectures based on performing projective measurements in the Greenberger-Horne-Zeilinger (GHZ) basis on constant-sized, entangled resource states. We present linear-optical constructions of the architectures, where the GHZ-state measurements are encoded to suppress the errors induced by photon loss and the probabilistic nature of linear optics. Simulations of our constructions demonstrate high single-photon loss thresholds compared to the state-of-the-art linear-optical architecture realized with encoded two-qubit fusion measurements performed on constant-sized resource states. We believe this result shows a resource-efficient path to achieving photonic fault-tolerant quantum computing

Saliva Viral Load Better Correlates with Clinical and Immunological Profiles in Children with Coronavirus Disease 2019

BACKGROUND: Pediatric COVID-19 studies exploring the relationships between NPS and saliva viral loads, clinical and immunological profiles are lacking. METHODS: Demographics, immunological profiles, nasopharyngeal swab (NPS), and saliva samples collected on admission, and hospital length of stay (LOS) were assessed in children below 18 years with COVID-19. FINDINGS: 91 patients were included between March and August 2020. NPS and saliva viral loads were correlated (r=0.315, p=0.01). Symptomatic patients had significantly higher NPS and saliva viral loads than asymptomatic patients. Serial NPS and saliva viral load measurements showed that the log10 NPS (r=-0.532, p<0.001) and saliva (r=-0.417, p<0.001) viral loads for all patients were inversely correlated with the days from symptom onset with statistical significance. Patients with cough, sputum, and headache had significantly higher saliva, but not NPS, viral loads. Higher saliva, but not NPS, viral loads were associated with total lymphopenia, CD3 and CD4 lymphopenia (all p<0.05), and were inversely correlated with total lymphocyte (r=-0.43), CD3 (r=-0.55), CD4 (r=-0.60), CD8 (r=-0.41), B (r=-0.482), and NK (r=-0.416) lymphocyte counts (all p<0.05). Interpretation: Saliva viral loads on admission in children correlated better with clinical and immunological profiles than NPS

Lack of Evidence for Human-to-Human Transmission of Avian Influenza A (H9N2) Viruses in Hong Kong, China 19991

In April 1999, isolation of avian influenza A (H9N2) viruses from humans was confirmed for the first time. H9N2 viruses were isolated from nasopharyngeal aspirate specimens collected from two children who were hospitalized with uncomplicated, febrile, upper respiratory tract illnesses in Hong Kong during March 1999. Novel influenza viruses have the potential to initiate global pandemics if they are sufficiently transmissible among humans. We conducted four retrospective cohort studies of persons exposed to these two H9N2 patients to assess whether human-to-human transmission of avian H9N2 viruses had occurred. No serologic evidence of H9N2 infection was found in family members or health-care workers who had close contact with the H9N2-infected children, suggesting that these H9N2 viruses were not easily transmitted from person to person