Quantum error correction (QEC) can overcome the errors experienced by qubits and is therefore an essential component of a future quantum computer. To implement QEC, a qubit is redundantly encoded in ...a higher-dimensional space using quantum states with carefully tailored symmetry properties. Projective measurements of these parity-type observables provide error syndrome information, with which errors can be corrected via simple operations. The 'break-even' point of QEC--at which the lifetime of a qubit exceeds the lifetime of the constituents of the system--has so far remained out of reach. Although previous works have demonstrated elements of QEC, they primarily illustrate the signatures or scaling properties of QEC codes rather than test the capacity of the system to preserve a qubit over time. Here we demonstrate a QEC system that reaches the break-even point by suppressing the natural errors due to energy loss for a qubit logically encoded in superpositions of Schrödinger-cat states of a superconducting resonator. We implement a full QEC protocol by using real-time feedback to encode, monitor naturally occurring errors, decode and correct. As measured by full process tomography, without any post-selection, the corrected qubit lifetime is 320 microseconds, which is longer than the lifetime of any of the parts of the system: 20 times longer than the lifetime of the transmon, about 2.2 times longer than the lifetime of an uncorrected logical encoding and about 1.1 longer than the lifetime of the best physical qubit (the |0〉f and |1〉f Fock states of the resonator). Our results illustrate the benefit of using hardware-efficient qubit encodings rather than traditional QEC schemes. Furthermore, they advance the field of experimental error correction from confirming basic concepts to exploring the metrics that drive system performance and the challenges in realizing a fault-tolerant system.
Shape memory polymers (SMPs) can retain a temporary shape after pre-deformation at an elevated temperature and subsequent cooling to a lower temperature. When reheated, the original shape can be ...recovered. Relatively little work in the literature has addressed the constitutive modeling of the unique thermomechanical coupling in SMPs. Constitutive models are critical for predicting the deformation and recovery of SMPs under a range of different constraints. In this study, the thermomechanics of shape storage and recovery of an epoxy resin is systematically investigated for small strains (within ±10%) in uniaxial tension and uniaxial compression. After initial pre-deformation at a high temperature, the strain is held constant for shape storage while the stress evolution is monitored. Three cases of heated recovery are selected: unconstrained free strain recovery, stress recovery under full constraint at the pre-deformation strain level (no low temperature unloading), and stress recovery under full constraint at a strain level fixed at a low temperature (low temperature unloading). The free strain recovery results indicate that the polymer can fully recover the original shape when reheated above its glass transition temperature (
T
g). Due to the high stiffness in the glassy state (
T
<
T
g), the evolution of the stress under strain constraint is strongly influenced by thermal expansion of the polymer. The relationship between the final recoverable stress and strain is governed by the stress–strain response of the polymer above
T
g. Based on the experimental results and the molecular mechanism of shape memory, a three-dimensional small-strain internal state variable constitutive model is developed. The model quantifies the storage and release of the entropic deformation during thermomechanical processes. The fraction of the material freezing a temporary entropy state is a function of temperature, which can be determined by fitting the free strain recovery response. A free energy function for the model is formulated and thermodynamic consistency is ensured. The model can predict the stress evolution of the uniaxial experimental results. The model captures differences in the tensile and compressive recovery responses caused by thermal expansion. The model is used to explore strain and stress recovery responses under various flexible external constraints that would be encountered in applications of SMPs.
The Schrodinger's cat thought experiment highlights the counterintuitive concept of entanglement in macroscopically distinguishable systems. The hallmark of entanglement is the detection of strong ...correlations between systems, most starkly demonstrated by the violation of a Bell inequality. No violation of a Bell inequality has been observed for a system entangled with a superposition of coherent states, known as a cat state. Here we use the Clauser-Horne-Shimony-Holt formulation of a Bell test to characterize entanglement between an artificial atom and a cat state, or a Bell-cat. Using superconducting circuits with high-fidelity measurements and real-time feedback, we detect correlations that surpass the classical maximum of the Bell inequality. We investigate the influence of decoherence with states up to 16 photons in size and characterize the system by introducing joint Wigner tomography. Such techniques demonstrate that information stored in superpositions of coherent states can be extracted efficiently, a crucial requirement for quantum computing with resonators.
Mass excesses of short-lived A ¼ 2Z 1 nuclei 63Ge, 65As, 67Se, and 71Kr have been directly measured to be 46 921ð37Þ, 46 937ð85Þ, 46 580ð67Þ, and 46 320ð141Þ keV, respectively. The deduced proton ...separation energy of 90ð85Þ keV for 65As shows that this nucleus is only slightly proton unbound. X-ray burst model calculations with the new mass excess of 65As suggest that the majority of the reaction flow passes through 64Ge via proton capture, indicating that 64Ge is not a significant rp-process waiting point.
► Study of resistance welding as a technique to join NiTi shape memory alloys thin-walled tubes. ► Study of the effect of post-welding thermomechanical treatment. ► Properties studied by DSC, ...microstructure observations and nanoindentation tests. ► Complex shape memory alloys structures with low density can be created using this technique.
Resistance welding is studied as a technique to join NiTi shape memory alloy thin-walled tubes. Properties of the welded metal are compared to those of the base metal by means of differential scanning calorimetry measurements, microstructure observations and nanoindentation tests. Transformation behaviour, microstructure and mechanical properties of the joint are significantly affected by the welding process. The effect of post-welding thermomechanical treatment is studied. After solution treatment followed by ageing, the transformation behaviour of the joint and of the initial material is almost identical. Strength of the joint is analysed by means of tensile and compression tests performed on as welded and heat treated tubes. This study proves that resistance welding is a feasible technique to create complex structures with low density and high reversible elasticity.
The paper examines terrestrial and oceanic carbon budgets from preindustrial time to present day in the version of Beijing Climate Center Climate System Model (BCC_CSM1.1) which is a global fully ...coupled climate‐carbon cycle model. Atmospheric CO2 concentration is calculated from a prognostic equation taking into account global anthropogenic CO2 emissions and the interactive CO2 exchanges of land‐atmosphere and ocean‐atmosphere. When forced by prescribed historical emissions of CO2 from combustion of fossil fuels and land use change, BCC_CSM1.1 can reproduce the trends of observed atmospheric CO2 concentration and global surface air temperature from 1850 to 2005. Simulated interannual variability and long‐term trend of global carbon sources and sinks and their spatial patterns generally agree with other model estimates and observations, which shows the following: (1) Both land and ocean in the last century act as net carbon sinks. The ability of carbon uptake by land and ocean is enhanced at the end of last century. (2) Interannual variability of the global atmospheric CO2 concentration is closely correlated with the El Niño‐Southern Oscillation cycle, in agreement with observations. (3) Interannual variation of the land‐to‐atmosphere net carbon flux is positively correlated with surface air temperature while negatively correlated with soil moisture over low and midlatitudes. The relative contribution of soil moisture to the interannual variation of land‐atmosphere CO2 exchange is more important than that of air temperature over tropical regions, while surface air temperature is more important than soil moisture over other regions of the globe.
Key Points
To evaluate BCC_CSM in reproducing the global carbon cycle from 1850 to 2005
To quantify the interannual to long‐term trend of carbon sources and sinks
To provide some discussions of BCC_CSM compared to other models
The inward rectifier K
+ channel Kir2.1 mediates the potassium
I
K1 current in the heart. It is encoded by
KCNJ2 gene that has been linked to Andersen’s syndrome. Recently, strong evidences showed ...that Kir2.1 channels were associated with mouse atrial fibrillation (AF), therefore we hypothesized that
KCNJ2 was associated with familial AF. Thirty Chinese AF kindreds were evaluated for mutations in
KCNJ2 gene. A valine-to-isoleucine mutation at position 93 (V93I) of Kir2.1 was found in all affected members in one kindred. This valine and its flanking sequence is highly conserved in Kir2.1 proteins among different species. Functional analysis of the V93I mutant demonstrated a gain-of-function consequence on the Kir2.1 current. This effect is opposed to the loss-of-function effect of previously reported mutations in Andersen’s syndrome. Kir2.1 V93I mutation may play a role in initiating and/or maintaining AF by increasing the activity of the inward rectifier K
+ channel.
A series of novel 3-arylethynyltriazolyl ribonucleosides were synthesized and assessed for their anticancer activity on the drug-resistant pancreatic cancer cell line MiaPaCa-2. Among them, one ...compound exhibited potent apoptosis-inducing properties and anticancer activity against the pancreatic cancer model MiaPaCa-2 both in vitro and in vivo with no adverse effects. This compound did not inhibit DNA synthesis and therefore does not resemble the clinical drug gemcitabine. It did, however, significantly down-regulate the expression of heat shock protein 27 (Hsp27), a small molecular chaperone playing an important role in drug resistance and highly expressed in drug-resistant cancer forms, and thus represents the first small molecular anticancer lead with such a mode of action.
Atrial fibrillation (AF) is the most common cardiac arrhythmia encountered in clinical practice. We first reported an S140G mutation of KCNQ1, an α subunit of potassium channels, in one Chinese ...kindred with AF. However, the molecular defects and cellular mechanisms in most patients with AF remain to be identified. We evaluated 28 unrelated Chinese kindreds with AF and sequenced eight genes of potassium channels (
KCNQ1, HERG, KCNE1, KCNE2, KCNE3, KCNE4, KCNE5, and
KCNJ2). An arginine-to-cysteine mutation at position 27 (R27C) of KCNE2, the β subunit of the KCNQ1-KCNE2 channel responsible for a background potassium current, was found in 2 of the 28 probands. The mutation was present in all affected members in the two kindreds and was absent in 462 healthy unrelated Chinese subjects. Similar to KCNQ1 S140G, the mutation had a gain-of-function effect on the KCNQ1-KCNE2 channel; unlike long QT syndrome–associated KCNE2 mutations, it did not alter HERG-KCNE2 current. The mutation did not alter the functions of the HCN channel family either. Thus, KCNE2 R27C is a gain-of-function mutation associated with the initiation and/or maintenance of AF.
Direct mass measurements of
78Kr projectile fragments have been performed in the recently commissioned storage ring CSRe employing the isochronous mass spectrometry method. A new data-analysis ...technique has been developed to correct the drifts in the revolution frequencies caused by instabilities of the magnetic fields in the CSRe, thus yielding a mass resolving power of
R
=
m
/
Δ
m
≈
1.7
×
10
5
(sigma). Masses for
45V,
47Cr,
49Mn and
51Fe nuclei are determined with a relative mass precision of
δ
m
/
m
≈
2
×
10
−
7
(sigma) which is an improvement by a factor of
∼
2
compared to the literature values.
PDF
