Fast radio bursts (FRBs) are millisecond-duration radio transients of unknown physical origin observed at extragalactic distances
. It has long been speculated that magnetars are the engine powering ...repeating bursts from FRB sources
, but no convincing evidence has been collected so far
. Recently, the Galactic magnetar SRG 1935+2154 entered an active phase by emitting intense soft γ-ray bursts
. One FRB-like event with two peaks (FRB 200428) and a luminosity slightly lower than the faintest extragalactic FRBs was detected from the source, in association with a soft γ-ray/hard-X-ray flare
. Here we report an eight-hour targeted radio observational campaign comprising four sessions and assisted by multi-wavelength (optical and hard-X-ray) data. During the third session, 29 soft-γ-ray repeater (SGR) bursts were detected in γ-ray energies. Throughout the observing period, we detected no single dispersed pulsed emission coincident with the arrivals of SGR bursts, but unfortunately we were not observing when the FRB was detected. The non-detection places a fluence upper limit that is eight orders of magnitude lower than the fluence of FRB 200428. Our results suggest that FRB-SGR burst associations are rare. FRBs may be highly relativistic and geometrically beamed, or FRB-like events associated with SGR bursts may have narrow spectra and characteristic frequencies outside the observed band. It is also possible that the physical conditions required to achieve coherent radiation in SGR bursts are difficult to satisfy, and that only under extreme conditions could an FRB be associated with an SGR burst.
Fast radio bursts (FRBs) are millisecond-duration radio transients
of unknown origin. Two possible mechanisms that could generate extremely coherent emission from FRBs invoke neutron star ...magnetospheres
or relativistic shocks far from the central energy source
. Detailed polarization observations may help us to understand the emission mechanism. However, the available FRB polarization data have been perplexing, because they show a host of polarimetric properties, including either a constant polarization angle during each burst for some repeaters
or variable polarization angles in some other apparently one-off events
. Here we report observations of 15 bursts from FRB 180301 and find various polarization angle swings in seven of them. The diversity of the polarization angle features of these bursts is consistent with a magnetospheric origin of the radio emission, and disfavours the radiation models invoking relativistic shocks.
Fast radio bursts (FRBs) are highly dispersed, millisecond-duration radio bursts1-3. Recent observations of a Galactic FRB4-8 suggest that at least some FRBs originate from magnetars, but the origin ...of cosmological FRBs is still not settled. Here we report the detection of1,863 bursts in 82 h over 54 days from the repeating source FRB 20201124A (ref.9). These observations show irregular short-time variation ofthe Faraday rotation measure (RM), which scrutinizes the density-weighted line-of-sight magnetic field strength, of individual bursts during the first 36 days, followed by a constant RM. We detected circular polarization in more than half of the burst sample, including one burst reaching a high fractional circular polarization of 75%. Oscillations in fractional linear and circular polarizations, as well as polarization angle as a function of wavelength, were detected. All of these features provide evidence for a complicated, dynamically evolving, magnetized immediate environment within about an astronomical unit (au; Earth-Sun distance) ofthe source. Our optical observations of its Milky-Way-sized, metal-rich host galaxy10-12 show a barred spiral, with the FRB source residing in a low-stellar-density interarm region at an intermediate galactocentric distance. This environment is inconsistent with a young magnetar engine formed during an extreme explosion of a massive star that resulted in a long gamma-ray burst or superluminous supernova.
Since the mid-20th century, nitrogen (N) deposition has shown an increasing trend in the Tibetan Plateau (TP), where alpine ecosystems are sensitive to elevated N deposition. However, the ...quantitative characterization of N deposition in the TP remains unclear, due in most part to the lack of in situ measurement. Using the Tibetan Observation and Research Platform network, we conducted short-term in situ measurements of major ions (NO3−, Cl−, SO42−, NH4+, Na+, K+, Ca2+, and Mg2+) wet deposition at five remote sites in the TP during 2011–2013. At Southeast Tibet Station, Nam Co Station, Qomolangma Station, Ngari Station, and Muztagh Ata Station, the NH4+–N wet deposition was 0.63, 0.68, 0.92, 0.36, and 1.25 kg N ha−1 yr−1, respectively; the NO3−–N wet deposition was 0.28, 0.24, 0.03, 0.08, and 0.30 kg N ha−1 yr−1, respectively; and the inorganic N wet deposition was 0.91, 0.92, 0.94, 0.44, and 1.55 kg N ha−1 yr−1, respectively. The inorganic N wet deposition mainly occurred in the form of NH4+–N during summer at all sites. Results of enrichment factor analysis and principal component analysis demonstrated that both NH4+–N and NO3−–N wet deposition in the TP were mainly influenced by anthropogenic activities. Backward trajectory analysis showed that the inorganic N deposition at Muztagh Ata Station was mainly transported from central Asia and the Middle East through westerlies. At Southeast Tibet Station, Nam Co Station, Qomolangma Station, and Ngari Station, the inorganic N deposition was mainly contributed by anthropogenic sources in south Asia, and was mainly transported by the Indian monsoon. Combining site-scale in situ measurements of inorganic N wet deposition in this and previous studies, the average wet deposition of atmospheric NH4+–N, NO3−–N, and inorganic N in the TP was estimated to be 1.06, 0.51, and 1.58 kg N ha−1 yr−1, respectively. The average NH4+–N : NO3−–N ratio in precipitation in the TP was approximately 2 : 1. Results from the present study suggest that earlier estimations based on chemical transport model simulations and/or limited field measurements likely overestimated substantially the regional inorganic N wet deposition in the TP. To clarify the total N deposition in the TP more clearly, it is essential to conduct long-term monitoring of both wet and dry deposition of atmospheric N in various climate zones in the TP in the future.
Geometric phases are noise resilient, and thus provide a robust way towards high-fidelity quantum manipulation. Here we experimentally demonstrate arbitrary nonadiabatic holonomic single-qubit ...quantum gates for both a superconducting transmon qubit and a microwave cavity in a single-loop way. In both cases, an auxiliary state is utilized, and two resonant microwave drives are simultaneously applied with well-controlled but varying amplitudes and phases for the arbitrariness of the gate. The resulting gates on the transmon qubit achieve a fidelity of 0.996 characterized by randomized benchmarking and the ones on the cavity show an averaged fidelity of 0.978 based on a full quantum process tomography. In principle, a nontrivial two-qubit holonomic gate between the qubit and the cavity can also be realized based on our presented experimental scheme. Our experiment thus paves the way towards practical nonadiabatic holonomic quantum manipulation with both qubits and cavities in a superconducting circuit.
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High tumor mutational burden (TMB-H) is correlated with enhanced objective response rate (ORR) and progression-free survival (PFS) for certain cancers receiving immunotherapy. This study aimed to ...investigate the safety and efficacy of toripalimab, a humanized programmed death-1 (PD-1) antibody, in advanced gastric cancer (AGC), and the predictive survival benefit of TMB and PD-L1.
We reported on the AGC cohort of phase Ib/II trial evaluating the safety and activity of toripalimab in patients with AGC, oesophageal squamous cell carcinoma, nasopharyngeal carcinoma and head and neck squamous cell carcinoma. In cohort 1, 58 chemo-refractory AGC patients received toripalimab (3 mg/kg d1, Q2W) as a monotherapy. In cohort 2, 18 chemotherapy-naive AGC patients received toripalimab (360 mg d1, Q3W) with oxaliplatin 130 mg/m2 qd, d1, capecitabine 1000 mg/m2 b.i.d., d1–d14, Q3W as first-line treatment. Primary end point was ORR. Biomarkers such as PD-L1 and TMB were evaluated for correlation with clinical efficacy.
In cohort 1, the ORR was 12.1% and the disease control rate (DCR) was 39.7%. Median PFS was 1.9 months and median OS was 4.8 months. The TMB-H group showed significant superior OS than the TMB-L group 14.6 versus 4.0 months, HR = 0.48 (96% CI 0.24–0.96), P = 0.038, while PD-L1 overexpression did not correlate with significant survival benefit. A 77.6% of patients experienced at least one treatment-related adverse event (TRAE), and 22.4% of patients experienced a grade 3 or higher TRAE. In cohort 2, the ORR was 66.7% and the DCR was 88.9%. A 94.4% of patients experienced at least one TRAE and 38.9% of patients experienced grade 3 or higher TRAEs.
Toripalimab has demonstrated a manageable safety profile and promising antitumor activity in AGC patients, especially in combination with XELOX. High TMB may be a predictive marker for OS of AGC patients receiving toripalimab as a single agent.
ClinicalTrials.gov NCT02915432.
Using geometric phases to realize noise-resilient quantum computing is an important method to enhance the control fidelity. In this work, we experimentally realize a universal nonadiabatic geometric ...quantum gate set in a superconducting qubit chain. We characterize the realized single- and two-qubit geometric gates with both quantum process tomography and randomized benchmarking methods. The measured average fidelities for the single-qubit rotation gates and two-qubit controlled-Z gate are 0.9977(1) and 0.977(9), respectively. Besides, we also experimentally demonstrate the noise-resilient feature of the realized single-qubit geometric gates by comparing their performance with the conventional dynamical gates with different types of errors in the control field. Thus, our experiment proves a way to achieve high-fidelity geometric quantum gates for robust quantum computation.
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Logical qubit encoding and quantum error correction (QEC) protocols have been experimentally demonstrated in various physical systems with multiple physical qubits, generally without reaching the ...break-even point, at which the lifetime of the quantum information exceeds that of the single best physical qubit within the logical qubit. Logical operations are challenging, owing to the necessary non-local operations at the physical level, making bosonic logical qubits that rely on higher Fock states of a single oscillator attractive, given their hardware efficiency. QEC that reaches the break-even point and single logical-qubit operations have been demonstrated using the bosonic cat code. Here, we experimentally demonstrate repetitive QEC approaching the break-even point of a single logical qubit encoded in a hybrid system consisting of a superconducting circuit and a bosonic cavity using a binomial bosonic code. This is achieved while simultaneously maintaining full control of the single logical qubit, including encoding, decoding and a high-fidelity universal quantum gate set with 97% average process fidelity. The corrected logical qubit has a lifetime 2.8 times longer than that of its uncorrected counterpart. We also perform a Ramsey experiment on the corrected logical qubit, reporting coherence twice as long as for the uncorrected case.Repeated error correction creates a logical qubit encoded in the hybrid state of a superconducting circuit and a bosonic cavity, which is shown to be fully controllable under a universal single-qubit gate set.
Searching topological states in artificial systems has recently become a rapidly growing field of research. Meanwhile, significant experimental progress on observing topological phenomena has been ...made in superconducting circuits. However, topological insulator states have not yet been reported in this system. Here, for the first time, we experimentally realize a tunable dimerized spin chain model and observe the topological magnon insulator states in a superconducting qubit chain. Via parametric modulations of the qubit frequencies, we show that the qubit chain can be flexibly tuned into topologically trivial or nontrivial magnon insulator states. Based on monitoring the quantum dynamics of a single-qubit excitation in the chain, we not only measure the topological winding numbers, but also observe the topological magnon edge and defect states. Our experiment exhibits the great potential of tunable superconducting qubit chain as a versatile platform for exploring noninteracting and interacting symmetry-protected topological states.
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