Search

Quantum measurements are a fundamental component of quantum computing. However, on present-day quantum computers, measurements can be more error prone than quantum gates and are susceptible to nonunital errors as well as nonlocal correlations due to measurement crosstalk. While readout errors can be mitigated in postprocessing, this is inefficient in the number of qubits due to a combinatorially large number of possible states that need to be characterized. In this work, we show that measurement errors can be tailored into a simple stochastic error model using randomized compiling, enabling the efficient mitigation of readout errors via quasiprobability distributions reconstructed from the measurement of a single preparation state in an exponentially large confusion matrix. We demonstrate the scalability and power of this approach by correcting readout errors without matrix inversion on a large number of different preparation states applied to a register of eight superconducting transmon qubits. Moreover, we show that this method can be extended to midcircuit measurements used for active feedback via quasiprobabilistic error cancellation, and we demonstrate the correction of measurement errors on an ancilla qubit used to detect and actively correct bit-flip errors on an entangled memory qubit. Our approach enables the correction of readout errors on large numbers of qubits and offers a strategy for correcting readout errors in adaptive circuits in which the results of midcircuit measurements are used to perform conditional operations on nonlocal qubits in real time.

The Kerr-cat qubit is a bosonic qubit in which multiphoton Schrödinger cat states are stabilized by applying a two-photon drive to an oscillator with a Kerr nonlinearity. The suppressed bit-flip rate with increasing cat size makes this qubit a promising candidate to implement quantum error correction codes tailored for noise-biased qubits. However, achieving strong light-matter interactions necessary for stabilizing and controlling this qubit has traditionally required strong microwave drives that heat the qubit and degrade its performance. In contrast, increasing the coupling to the drive port removes the need for strong drives at the expense of large Purcell decay. By integrating an effective band-block filter on chip, we overcome this trade-off and realize a Kerr-cat qubit in a scalable 2D superconducting circuit with high coherence. This filter provides 30 dB of isolation at the qubit frequency with negligible attenuation at the frequencies required for stabilization and readout. We experimentally demonstrate quantum nondemolition readout fidelity of 99.6% for a cat with eight photons. Also, to have high-fidelity universal control over this qubit, we combine fast Rabi oscillations with a new demonstration of the X(π/2) gate through phase modulation of the stabilization drive. Finally, the lifetime in this architecture is examined as a function of the cat size of up to ten photons in the oscillator, achieving a bit-flip time higher than 1 ms and only a linear increase in the phase-flip rate, in good agreement with the theoretical analysis of the circuit. Our qubit shows promise as a building block for fault-tolerant quantum processors with a small footprint.

Abstract Hybridization is one of the most fundamental quantum mechanical phenomena, with the text book example of binding two hydrogen atoms in a hydrogen molecule. Here we report tunnel spectroscopy experiments illustrating the hybridization of another type of discrete quantum states, namely of superconducting subgap states that form in segments of a semiconducting nanowire in contact with superconducting reservoirs. We discuss a collection of intermediate states with unique (tunnel) spectroscopic fingerprints in the process of merging well-known individual bound states, hybridized by a central quantum dot and eventually coherently linking the reservoirs, carrying a Josephson current. These coupled and fused Andreev bound states can be seen as superconducting analogues to atomic and molecular single electron states in nature, and explain a variety of recent bound state spectra, with specific fingerprints that will have to be winnowed in future Majorana fusion experiments.

Abstract Ternary quantum information processing in superconducting devices poses a promising alternative to its more popular binary counterpart through larger, more connected computational spaces and proposed advantages in quantum simulation and error correction. Although generally operated as qubits, transmons have readily addressable higher levels, making them natural candidates for operation as quantum three-level systems (qutrits). Recent works in transmon devices have realized high fidelity single qutrit operation. Nonetheless, effectively engineering a high-fidelity two-qutrit entanglement remains a central challenge for realizing qutrit processing in a transmon device. In this work, we apply the differential AC Stark shift to implement a flexible, microwave-activated, and dynamic cross-Kerr entanglement between two fixed-frequency transmon qutrits, expanding on work performed for the Z Z interaction with transmon qubits. We then use this interaction to engineer efficient, high-fidelity qutrit CZ† and CZ gates, with estimated process fidelities of 97.3(1)% and 95.2(3)% respectively, a significant step forward for operating qutrits on a multi-transmon device.

The exploration of highly connected networks of qubits is invaluable for implementing various quantum algorithms and simulations, as it allows for entangling qubits with reduced circuit depth. Here, we demonstrate a multiqubit sideband tone-assisted Rabi-driven gate. Our scheme is inspired by the ion-qubit Mølmer-Sørensen gate and is mediated by a shared photonic mode and Rabi-driven superconducting qubits, which relaxes restrictions on qubit frequencies during fabrication and supports scalability. We achieve a two-qubit gate with a maximum state fidelity of 95% in 310 ns, a three-qubit gate with a state fidelity of 90.5% in 217 ns, and a four-qubit gate with a state fidelity of 66% in 200 ns. Furthermore, we develop a model of the gate that shows that the four-qubit gate is limited by shared resonator losses and the spread of qubit-resonator couplings, which must be addressed to reach high-fidelity operations.

Transforming stand-alone qubits into a functional, general-purpose quantum processing unit requires an architecture where many-body quantum entanglement can be generated and controlled in a coherent, modular, and measurable fashion. Electronic circuits promise a well-developed pathway for large-scale integration once a mature library of quantum-compatible elements have been developed. In the domain of superconducting circuits, fluxonium has recently emerged as a promising qubit due to its high-coherence and large anharmonicity, yet its scalability has not been systematically explored. In this work, we present a blueprint for a high-performance fluxonium-based quantum processor that addresses the challenges of frequency crowding, and both quantum and classical crosstalk. The main ingredients of this architecture include high-anharmonicity circuits, multipath couplers to entangle qubits where spurious longitudinal coupling can be nulled, circuit designs that are compatible with multiplexed microwave circuitry, and strongly coupled readout channels that do not require complex, frequency-sculpted elements to maintain coherence. In addition, we explore robust and resource-efficient protocols for quantum logical operations, then perform numerical simulations to validate the expected performance of this proposed processor with respect to gate fidelity, fabrication yield, and logical error suppression. Lastly, we discuss practical considerations to implement the architecture and achieve the anticipated performance.

In the FCTRAC project, a fuel cell electric tractor is developed based on the existing diesel vehicle STEYR 4130 Expert CVT. After the FCTRAC project is presented, the paper introduces the developed fuel cell electric powertrain architecture designed to deliver comparable working performance to the donor vehicle. The description of the thermal system focuses on the challenging heat dissipation of the fuel cell stack. The design of the 700-bar hydrogen storage system is discussed, considering vehicle framework conditions. Finally, the paper addresses the test bench validation of the FCTRAC powertrain. It confirms the simulative development approach and demonstrates operation comparable to the donor vehicle with 95 kW constant load at 35 °C ambient temperature without derating.

We present a comprehensive electrical characterization of an InAs/InP nanowire (NW) heterostructure, comprising of two InP barriers forming a quantum dot (QD), two adjacent lead segments and two metallic contacts. We demonstrate how to extract valuable quantitative information of the QD. The QD shows very regular Coulomb blockade resonances over a large gate voltage range. By analyzing the resonance line shapes, we map the evolution of the tunnel couplings from the few to the many electron regime, with electrically tunable tunnel couplings from <1 μeV to >600 μeV, and a transition from the temperature to the lifetime broadened regime. The InP segments form tunnel barriers with almost fully symmetric tunnel couplings and a barrier height of ∼350 meV. All of these findings can be understood in great detail based on the deterministic material composition and geometry. Our results demonstrate that integrated InAs/InP QDs provide a promising platform for electron tunneling spectroscopy in InAs NWs, which can readily be contacted by a variety of superconducting materials to investigate subgap states in proximitized NW regions, or be used to characterize thermoelectric nanoscale devices in the quantum regime. [ABSTRACT FROM AUTHOR]

A holistic understanding and careful balancing of different quality aspects can support sustainable, evidence-based decisions during the planning and realisation phases of a building. To this end, it is important to consider, whether and to what extent different quality aspects are interrelated in order to assess potential consequences of decisions. For this purpose, the Holistic Quality Model 2.0 is introduced, representing a second iteration of the Holistic Quality Model developed in recent studies. It incorporates two improvements. First, the integration of the economic quality aspect in addition to the technical, environmental and social quality aspects. Second, the development of an extended interrelations methodology to facilitate better identification and quantitative analysis of interrelations. These improvements and a corresponding case study emphasise the shift from the conventional practice of evaluating quality aspects in isolation towards a holistic approach enabling informed decision-making by considering and balancing different quality aspects.

Construction logistics is an influential participant in the overall urban freight network and a bottle neck for an efficient construction process. Especially in the urban area professionalization of its management may reduce negative impacts on the environment from which stakeholders, like construction companies, policymakers and residents, do profit. In order to shed light on construction logistics in the urban environment in particular, a two-step methodological approach was pursued, which reconciles scientific findings with consideration in policies for the first time. Therefore, the current state of research was investigated by performing a systematic literature review and applying bibliometric keyword co-occurrence analyses in the first place. Moreover, policy papers (grey literature) on urban freight transportation of the 20 biggest cities in the DACH-region (Germany, Austria, Switzerland) were analyzed for their consideration of construction logistics in an initial case study. The results demonstrate limited consideration with only four cities paying deliberate attention within their overall logistics policy concepts and just one city providing construction logistics-specific policy recommendations. This is in line with the findings that although construction logistics in the urban environment is an emerging topic in academia, it is currently underrepresented in the context of urban logistics research. Therefore, combined results suggest insufficient translation of research findings into actionable policies despite existing literature providing possible ways to design future policies, e.g., by supporting decision-making. In conclusion, strategic management of construction logistics in the urban environment should be paid more attention to from both policy and academia in proportion to its environmental and socio-economic effects as well as its impact on the whole construction process. In that regard, predominately robust empirical data is needed in order to legitimate effective and sustainable concepts for urban construction logistics for both public and private actors.

Digital technologies are being introduced in all areas of the construction industry with the overarching goals of increasing productivity while simultaneously simplifying work and reducing errors. Nevertheless, their use and the associated implementation in construction companies is currently still inhibited. One reason for this is the lack of a holistic implementation process for digital technologies. Therefore, the aim of this paper is to deliver a concept for such a holistic digital-technology-implementation-process which addresses current barriers. For this purpose, a qualitative literature analysis was conducted first, which reveals the current focus of research on digital technologies. In a second step, current barriers regarding the implementation of digital technologies were identified by conducting interviews with experts from German construction companies. The interview concept combined and adapted the survey instruments Technology Commitment by Neyer et al. and Technophobia by Sinkovics. Based on the findings of the qualitative literature research and the expert interviews, a holistic implementation process for the introduction of digital technologies for construction companies was developed, which specifically addresses the currently prevailing barriers. Therefore, the barriers Acceptance, Control and Competence were classified in a temporal context within the implementation process and recommendations for action are presented for the individual process steps of implementing digital technologies.