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The magnetic-flux analogue to coherent Josephson tunnelling of electric charge has been observed in a strongly disordered superconducting nanowire.

One of the advantages that it is hoped quantum computers will have over classical computers is their ability to accurately simulate quantum phenomena. Silveri et al.take a step towards this goal by simulating so-called motional averaging in an artificial atom realized by a superconducting quantum bit.

Interrupting a superconducting loop with a thin ferromagnetic film creates a so-called π-Josephson junction that shifts the phase of a current flowing in the loop by 180°. A demonstration of the use of π-junctions in a variety of device structures suggests they could enable the development of a new class of superconducting logic circuits.

Excitonic condensation occurs when electrons and holes in closely placed bilayers form bound pairs and condense into a coherent quantum state. This Perspective highlights recent experimental breakthroughs and emerging directions in the rapidly evolving field of excitonic condensation in van der Waals bilayer systems.

The authors demonstrate a simple direct-current-measurement characterization of a quarter-wavelength superconducting coplanar waveguide resonator using an on-chip bolometer. This approach offers simpler experimental instrumentation and much larger frequency range of operation compared to traditional RF techniques.

A lasing effect with a single artificial atom (a Josephson-junction charge qubit) that is embedded in a superconducting resonator is demonstrated, making use of the property that such artificial atoms are strongly and controllably coupled to resonator modes. The device is essentially different from existing lasers and masers; one and the same artificial atom excited by current injection produces many photons.

Quantum state engineering necessitates transfer between quantum states. Here the authors demonstrate coherent population transfer between un- or weakly-coupled states of solid state systems, superconducting Xmon and phase qutrits, using stimulated Raman adiabatic passage and microwave driving.

A quasiparticle in Andreev levels was coupled to a superconducting microwave resonator and its spin was monitored in real time. This has potential applications in the readout of superconducting spin qubits and measurements of Majorana fermions.

Experiments show that electron waves can be confined to and guided along the edges of monolayer and bilayer graphene sheets, analogous to the guiding of light waves in optical fibres.

Cavity QED systems which can be used for quantum information processing can absorb or emit signals with specific frequencies and temporal envelops. Here, the authors show that the temporal and spectral content of microwave signals can be manipulated with a flexible aluminium drumhead embedded in a circuit.

A circuit consisting of four superconducting diodes implemented in niobium nitride thin film on a single chip can achieve alternating to direct current conversion with 50 MHz signals in periodic bursts.

Accurately characterizing the noise influencing quantum devices is instrumental to improve coherence properties and design more robust control protocols. Sung et al. demonstrate non-Gaussian noise spectroscopy with a superconducting qubit, enabling the detection and characterization of dephasing noise without assuming Gaussian statistics.

I. Silber et al. discover a two-fold symmetry of the superconducting upper critical field in hexagonal 4Hb-TaS₂ just below T_c, a clear signature of nematic, two-component superconductivity. They further suggest a theoretical model that reconciles the nematic superconductivity with the previously-observed time-reversal-symmetry-breaking in this material.

The approach to stabilizing a quantum state by coupling to engineered reservoirs is limited by a trade-off between state fidelity and stabilization rate. Here the authors implement a protocol based on parametric system-bath coupling to achieve fast and high-fidelity Bell state stabilization in a qutrit-qubit system.

Gate-tunable superconducting quantum interference devices can be created in the two-dimensional superconductor formed at oxide interfaces.

Research on superconductivity in magic-angle twisted bilayer graphene reveals unconventional behaviour, an anisotropic gap and a significant role of quantum geometry, using combined d.c. transport and microwave measurements, suggesting new insights into superconductivity mechanisms.

The authors employ zero-field muon spin relaxation to study time-reversal symmetry breaking (TRSB) in FeSe_1−xTe_x. For x = 0.64 with the highest superconducting transition temperature T_c = 14.5 K, which is known to host a topological surface state and Majorana zero modes within vortices, they find a TRSB superconducting state in the bulk.

The motion of magnetic vortices induced in type-II superconductors by a magnetic field degrades their ability to conduct electricity with zero resistance. Córdoba et al.demonstrate a means to immobilize these vortices, reversing their deleterious effect as the applied magnetic field is increased.

Controlling the motion and pinning of vortices is essential for developing superconducting electronics. Here, the authors reveal the vortex pinning nano-network in thin superconducting niobium films by developing a scanning quantum vortex microscopy approach.

Spin-momentum locking is a fundamental property of condensed matter systems. Here, the authors evidence parallel Weyl spin-momentum locking of multifold fermions in the chiral topological semimetal PtGa.

Exciton-polariton condensates are hybrid systems with nonlinear interactions. Here the authors demonstrate metamaterials with inter-site polariton coupling and asynchronous locking of light fluids from neighbor sites at the energy detuning.

Hall resistance quantization measurements in the quantum anomalous Hall effect regime on a device based on the magnetic topological insulator V-doped (Bi,Sb)₂Te₃ show that the system can provide a zero external magnetic field quantum standard of resistance.

Josephson junctions based on graphene exhibit tunable proximity effects. The appearance of superconducting states when changing magnetic field and carrier concentration has now been investigated—some proximity effect survives for fields above 1 T.

Hybrid quantum acoustic systems integrating qubits with phonons offer a novel platform for investigating open quantum systems. Kitzman et al. report control of superposition states of a transmon qubit under the effect of drive and dissipation by engineering its coupling to a bath of surface acoustic wave phonons.

Superconducting qubits are measured using microwaves, posing constraints on its size and thermal budgets. The electro-optic transceiver presented here can be used to perform optical readout without affecting qubit performance.

The non-volatile switching of tunnel electroresistance in ferroelectric junctions provides the basis for memory and neuromorphic computing devices. Rouco et al. show tunnel electroresistance in superconductor-based junctions that arises from a redox rather than ferroelectric mechanism and is enhanced by superconductivity.

A thermal detector based on a graphene monolayer operates at the threshold for circuit quantum electrodynamics applications, achieving a minimum time constant of 200 ns.

Artificial atoms, quantum systems with atom-like energy structure, have been studied with frequency spectroscopic techniques. However, much information about the energy level spectrum has been hidden, as the technique is impractical for high frequencies. A complementary technique has been developed where the energy level of an artificial atom is not scanned by tuning frequency, but amplitude of the radiation, while the frequency is tuned to a specific feature in the spectrum.

The quantum light–matter interaction between a superconducting artificial atom and squeezed vacuum reduces the transverse radiative decay rate of the atom by a factor of two, allowing the corresponding coherence time, T₂, to exceed the ordinary vacuum decay limit, 2T₁.

Quantum computers based on superconducting transmon qubits are limited by single qubit lifetimes and coherence times, which are orders of magnitude shorter than limits imposed by bulk material properties. Here, the authors fabricate two-dimensional transmon qubits with both lifetimes and coherence times longer than 0.3 milliseconds by replacing niobium with tantalum in the device.

A study of autoresonant behaviour in a superconducting quantum pendulum reveals that fluctuations, both quantum and classical, only determine the initial oscillator motion, not its subsequent dynamics.

Chiral superconductors are very rare topological materials. Here, the authors report spontaneous magnetic fields inside the superconducting state and low temperature linear behavior in the superfluid density in LaPt₃P, suggesting a chiral d-wave singlet superconducting state.

Measurements of the superfluid stiffness in twisted trilayer graphene reveal unconventional nodal-gap superconductivity, where the superconducting transition is controlled by phase fluctuations rather than Cooper-pair breaking.

Strong quadratic coupling between the motion of a membrane and the energy states of a qubit enables the creation of a non-classical energy-squeezed state in the mechanical oscillator.

High-fidelity control and readout of a superconducting qubit is performed with a low-noise optical fibre link that delivers microwave signals directly to the millikelvin quantum computing environment.

Fabricating tiny mechanical structures where the vibrational motion is purely quantum mechanical is a long-standing goal in physics, and a parallel goal is the development of a scheme for observing and controlling such tiny motions. By coupling a tiny mechanical resonator to a superconducting two-level quantum system (qubit), the state of the superconducting qubit can be measured through its influence on the vibrations of the resonator, a demonstration of nanomechanical read-out of quantum interference.