Quantum many-body systems display rich phase structure in their low-temperature equilibrium states
. However, much of nature is not in thermal equilibrium. Remarkably, it was recently predicted that ...out-of-equilibrium systems can exhibit novel dynamical phases
that may otherwise be forbidden by equilibrium thermodynamics, a paradigmatic example being the discrete time crystal (DTC)
. Concretely, dynamical phases can be defined in periodically driven many-body-localized (MBL) systems via the concept of eigenstate order
. In eigenstate-ordered MBL phases, the entire many-body spectrum exhibits quantum correlations and long-range order, with characteristic signatures in late-time dynamics from all initial states. It is, however, challenging to experimentally distinguish such stable phases from transient phenomena, or from regimes in which the dynamics of a few select states can mask typical behaviour. Here we implement tunable controlled-phase (CPHASE) gates on an array of superconducting qubits to experimentally observe an MBL-DTC and demonstrate its characteristic spatiotemporal response for generic initial states
. Our work employs a time-reversal protocol to quantify the impact of external decoherence, and leverages quantum typicality to circumvent the exponential cost of densely sampling the eigenspectrum. Furthermore, we locate the phase transition out of the DTC with an experimental finite-size analysis. These results establish a scalable approach to studying non-equilibrium phases of matter on quantum processors.
Practical quantum computing will require error rates well below those achievable with physical qubits. Quantum error correction
offers a path to algorithmically relevant error rates by encoding ...logical qubits within many physical qubits, for which increasing the number of physical qubits enhances protection against physical errors. However, introducing more qubits also increases the number of error sources, so the density of errors must be sufficiently low for logical performance to improve with increasing code size. Here we report the measurement of logical qubit performance scaling across several code sizes, and demonstrate that our system of superconducting qubits has sufficient performance to overcome the additional errors from increasing qubit number. We find that our distance-5 surface code logical qubit modestly outperforms an ensemble of distance-3 logical qubits on average, in terms of both logical error probability over 25 cycles and logical error per cycle ((2.914 ± 0.016)% compared to (3.028 ± 0.023)%). To investigate damaging, low-probability error sources, we run a distance-25 repetition code and observe a 1.7 × 10
logical error per cycle floor set by a single high-energy event (1.6 × 10
excluding this event). We accurately model our experiment, extracting error budgets that highlight the biggest challenges for future systems. These results mark an experimental demonstration in which quantum error correction begins to improve performance with increasing qubit number, illuminating the path to reaching the logical error rates required for computation.
Platinum is lost as gaseous PtO2 from the Pt-Rh (typically 95:5 wt%) catalyst used in the ammonia oxidation process. The most common technology utilized today for recovering PtO2 from the gas stream ...is to apply Pd-Ni (95:5 wt%) catchment gauzes. However, the technology suffers due to loss of Pd at the same time as a severe reconstruction of the alloy creates a large pressure drop during operation. In the search of alternative materials, LaNiO3 is considered as an interesting Pt catchment material. The evaluation is based on lab-scale Pt catchment experiments in a gas flow of dry air using a six-zone furnace with a Pt source placed at 1000 °C to create gaseous PtO2, and LaNiO3 pellets placed downstream at 700 – 900 °C. The duration of the experiments varied from 1 to 26 days, and scanning electron microscopy – energy dispersive X-ray analysis and powder X-ray diffraction were utilized to prove the catchment of Pt. The key finding is that LaNiO3 captures Pt and transforms via the non-stoichiometric rhombohedral LaNi1−xPtxO3 (x ≤ 0.075) and monoclinic La2Ni2−2xPt2xO6 (0.20 ≤ x < 0.50) perovskites into La2NiPtO6 (x = 0.50). Pt catchment is poor at 700 °C, but a substantial activity is documented at 800 and 900 °C. We furthermore demonstrate the recovery of Pt from the oxide by a wet chemical approach, and both LaNiO3 and La2NiPtO6 have been tested as potential catalysts for decomposition of NOx and N2O at relevant temperatures. LaNiO3 is not catalytically active in decomposition of NOx, the main ammonia oxidation products, while La2NiPtO6 has a minor catalytic activity toward NOx decomposition (1–2 %). However, both materials decompose the greenhouse gas N2O fully at 900 °C.
Display omitted
•LaNiO3 captures PtO2 at temperatures relevant for industrial HNO3 production.•LaNiO3 transforms into La2NiPtO6 during PtO2 catchment.•High levels of Pt in the formed La2NiPtO6 are recoverable by dissolution.•LaNiO3 and La2NiPtO6 have low activity towards NO loss.•A new family of Pt catchment materials relevant for HNO3 production is identified.
Transient liquid phase (TLP) bonding of 6063 aluminum alloy (Al-6063) and duplex alloy 2304 stainless steel (UNS S32304) was performed using copper foil as an interlayer between the base metals. A ...compression load was applied normal to the specimens. Metallurgical examination of the produced joints showed three distinct regions including a reaction zone, diffusion affected zone, and the base metals. The diffusion of copper into aluminum resulted in an Al–Cu eutectic structure. However, the oxide layer on the aluminum surface controlled the dissolution behavior of copper and the extent of its wettability with the base metals. Although voids and intermetallic compounds were detected at the interfaces of the processed joints, a defect free joint was produced at 570 °C. In addition, the results from corrosion tests showed that the use of copper as an interlayer decreased the corrosion resistance of the joints. However, increase in thickness of the joining reaction zone with increasing bonding temperature was observed to increase corrosion resistance.
Using non-$c$-plane bulk GaN substrates, we demonstrate continuous-wave single-mode blue-emitting laser diodes operating with over 23% wall plug efficiency and over 750 mW output power, which ...represent the highest values reported to date. Furthermore, we demonstrate continuous-wave 520 nm green-emitting laser diodes with over 60 mW output power and 1.9% wall plug efficiency. The rapid performance evolution of laser diodes fabricated on non-$c$-plane orientations is validation of the benefits resulting from increased electron--hole overlap, reduced effective hole mass, and increased design flexibility.
By means of a Gleeble machine, the flow stress at steady-state creep in an AA3103 aluminium alloy has been measured for temperatures and strain rates relevant for thermally induced deformations in DC ...casting. The strain rate has been determined by measuring the global radial strain rate at the specimen center by an extensometer, and the stress has been set equal to the force in the axial direction divided by the cross-section area. The parameters of Garofalo's equation have been fitted to the resulting steady-state stress and strain rate. Such a method is based upon the assumption of homogeneous stress and strain rate fields. In the Gleeble machine, the specimens are heated by the Joule effect leading to axial temperature gradients, and the specimen geometry is noncylindrical. The resulting inhomogeneities in the stress and strain rate fields are studied by finite element modeling, and it is shown that although they can be significant, the global radial strain rate and the axial force divided by the cross-section area at the specimen center can be relatively close to what the respective strain rate and stress values would have been if the conditions actually were homogeneous.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
PDF
