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Parametric phase-locked oscillators were first developed in the 1950s as a way of electrically storing and controlling information. Lin et al.now show that a modern version of this concept using superconducting circuits enables high-fidelity, single-shot and non-destructive measurement of a qubit.

Spin-entangled electron pairs are one possible resource for future solid-state quantum information processing systems. Here, the authors directly prove spin entanglement between two electrons that had previously been a Cooper pair in a superconducting lead but were split using two quantum dots.

A topological insulator-based Josephson junction is expected to host low-energy Andreev-bound states. Here, Kurter et al. study Josephson interferometry and SQUID oscillations in Bi₂Se₃junctions to evidence anomalous non-sinusoidal supercurrent contributions as possible signatures of these states.

A transmon qubit insensitive to magnetic fields is a crucial element in topological quantum computing. Here, Kroll et al. create graphene transmons by integrating monolayer graphene Josephson junctions into microwave frequency superconducting circuits, allowing them to operate in a parallel magnetic field of 1 T.

A material weakly linking two superconductors may itself exhibit superconductivity whilst its material properties strongly influence the nature of the supercurrent. Here, the authors identify a supercurrent with p-wave symmetry in such a Josephson junction made of topologically non-trivial material.

The standard current–phase relation in tunnel Josephson junctions involves a single sinusoidal term, but real junctions are more complicated. The effects of higher Josephson harmonics have now been identified in superconducting qubit devices.

J.-K. Kim et al. study vertical Josephson junctions where the weak link is T_d-WTe₂ and the superconductor is NbSe₂. The use of an inversion-symmetry-breaking T_d-WTe₂ weak link allows the authors to demonstrate the intrinsic origin of the observed Josephson non-reciprocity in these devices.

Van der Waals structures provide a new platform to explore novel physics of superconductor/ferromagnet interfaces. Here, NbSe₂ Josephson junction with Cr₂Ge₂Te₆ enables non-trivial Josephson phase by spin-dependent interaction, boosting the study of superconducting states with spin-orbit coupling and phase-controlled quantum electronic device.

An ultimately thin microwave bolometric sensor based on a superconductor–graphene–superconductor Josephson junction with monolayer graphene has a sensitivity approaching the fundamental limit imposed by intrinsic thermal fluctuations.

The authors study transport in Nb-(Pt/Cu)-Nb Josephson junctions (JJ), where Pt/Cu is a Rashba interface. Due to the Rashba–Edelstein effect, a charge current leads to a non-equilibrium spin moment at the Pt/Cu interface, which can be measured from a shift of the Fraunhofer pattern of the JJ.

A diode effect—asymmetric transport depending on its direction—is shown in the proximity-induced superconducting state of a Dirac semimetal.

Correlated electronic states in moiré matter are of great fundamental and technological interest. Here, the authors demonstrate a Josephson junction in magic-angle twisted bilayer graphene with a correlated insulator weak link, showing magnetism and programmable superconducting diode behaviour.

A Josephson diode is made by fabricating an inversion symmetry breaking van der Waals heterostructure of NbSe₂/Nb₃Br₈/NbSe₂, demonstrating that even without a magnetic field, the junction can be superconducting with a positive current but resistive with a negative current.

The fractional alternating-current Josephson effect produces a series of steps in the current–voltage characteristics of a superconducting junction driven at radiofrequencies. This unusual phenomenon is now observed in a semiconductor–superconductor nanowire. What is more, a doubling in step size when a strong magnetic field is applied could be a possible signature of Majorana fermions, particles that are their own antiparticle.

High-quality superconducting tunnel junctions operating above liquid nitrogen temperatures can be fabricated with a focused beam of helium ions that directly writes tunnel barriers in a cuprate superconductor.

Heterostructures of graphene and a superconducting metal allow Josephson junctions to be studied in a regime characterized by ballistic transport.

The observation of a superconductive current flowing through a topological insulator is considered the first step towards the observation of the elusive Majorana fermions. This is now achieved in a superconductor/topological insulator/superconductor junction in which direct evidence of Josephson supercurrents is reported.

An array of 488 Josephson junctions that amplifies and squeezes noise beyond conventional quantum limits should prove useful in the study and development of superconducting qubits and other quantum devices.

In situ electrostatic control of two-dimensional superconductivity is commonly limited due to large charge carrier densities. Now, by means of local gates, electrostatic gating can define a Josephson junction in a magic-angle twisted bilayer graphene device, a single-crystal material.

This work reports on the observation of a large Josephson diode effect in a type-II Dirac semimetal 1T-PtTe₂. The magnitude of the Josephson diode effect is found to be related to an asymmetry of the critical supercurrent which is modeled as a phase shift between the first and second harmonic terms of the current-phase relationship and can be tuned by an external magnetic field.

We show that domain walls in minimally twisted bilayer graphene support exceptionally robust proximity superconductivity in the quantum Hall regime.

Gatemons, or gate-tunable transmons, are superconducting qubits based on hybrid Josephson junctions, which typically use extended quantum conductors as weak links. Here the authors report a gatemon made with a carbon-nanotube-based junction, showing improved coherence time compared to graphene-based devices.

A unified realization of the volt, ohm and ampere can be achieved by integrating a quantum anomalous Hall resistor and a programmable Josephson voltage standard in a single cryostat.

Here, the authors demonstrate an array of superconducting qubits embedded into a microwave transmission line. They show that the transmission through the metamaterial periodically depends on externally applied magnetic field and suppression of the transmission is achieved through field-induced transitions.

The mechanisms behind the superconducting phase in magic-angle twisted bilayer graphene (MATBG) remain debated. Here, the authors investigate radio frequency-biased Josephson junctions in MATBG, providing insights into the electron-phonon coupling and superfluid stiffness of correlated electrons.

The authors fabricate a fluxonium circuit using a granular aluminium nanoconstriction to replace the conventional superconductor–insulator–superconductor tunnel junction. Their characterization suggests that this approach will be a useful element in the superconducting qubit toolkit.

A nonlinear transmission line that supports travelling-wave parametric amplification of forward propagating signals and isolation via the frequency conversion of backward propagating signals could be integrated on chip with superconducting qubits and could reduce the hardware overhead in superconducting quantum computers.

Atomic-resolution imaging of a strongly inhomogeneous superfluid in an iron-based superconductor shows spatial correlation between superfluid density variations and the strength of quasiparticle character.

The absence of a bandgap in the electronic spectrum of graphene can be overcome by breaking its lattice symmetry. The authors show that the insulating state of gapped graphene is electrically shorted by narrow edge channels exhibiting high conductivity.

Hybrid superconductor-semiconductor devices offer a promising platform for topological superconductivity. Here, Ke and Moehle et al. create ballistic Josephson junctions in InSb quantum wells and use magnetic and electric fields to control their free energy landscape.

Superconducting circuits are promising for quantum computing, but quasiparticle tunnelling across Josephson junctions introduces qubit decoherence. Ristè et al. convert a transmon qubit into its own real-time quasiparticle tunnelling detector and accurately measure induced decoherence in the millisecond range.

Scanned Josephson tunnelling microscopy is used to image Cooper pair tunnelling from a superconducting microscope tip to the quantum condensate of Bi₂Sr₂CaCu₂O_8+x, thus revealing the spatially modulated density of Cooper pairs predicted from several theories of the cuprate pseudogap phase.

An ideal amplifier has low noise, operates over a broad frequency range and has large dynamic range. A superconducting-resonator-based amplifier that combines all of these qualities is now demonstrated. The concept is applicable throughout the microwave, millimetre-wave and submillimetre-wave bands and can achieve a noise limit very close to that set by quantum mechanics.

At low temperatures, a superconducting current that flows through a graphene layer sandwiched between two superconducting electrodes can be carried by either electrons or by holes, depending on the gate voltage that determines the charge density in the graphene layer. Interestingly, this finds that a finite supercurrent can flow even when the charge density is zero.

The hybrid architecture of Andreev spin qubits made using semiconductor–superconductor nanowires means that supercurrents can be used to inductively couple qubits over long distances.

Efficient control and measurement of qubits requires them to be strongly coupled to other degrees of freedom, but this can introduce additional decoherence. Now, parametric driving makes it possible to controllably introduce and remove interactions.

Semiconductor qubits can benefit from existing industrial methods, but there are challenges in coupling qubits together. A hybrid superconductor–semiconductor qubit that couples to superconducting qubit devices may overcome these issues.

The trade-off between long lifetime and inevitable radiative decay to a control line has become a key limitation for superconducting qubits. Here, the authors break the trade-off by coupling another qubit to the control line of the first one to suppress its relaxation, while enabling fast qubit control.

The evolution of a quantum state undergoing radiative decay depends on how the emission is detected. Here, the authors demonstrate how continuous field detection, as opposed to the more common detection of energy quanta, allows control of the back-action on the emitter’s state.

Tests of the Bell-Kochen-Specker theorem aim at showing that the measurement statistics of a single qutrit are incompatible with noncontextual realism. Here, the authors use a superconducting qutrit with deterministic readouts to violate a noncontextuality inequality, ruling out several loopholes.