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Characterisation of quantum operations is fundamental in quantum technologies - quantum computing in particular - but there’s currently no reliably efficient method to assess mid-circuit measurements, which are a key component for subfields like quantum error correction. Here, the authors fill this gap, integrating MCMs into the framework of randomized benchmarking.

Shallow NV centers in diamond are promising quantum sensors but suffer from reduced coherence times due to surface spin impurities. Here the authors improve coherence times to over 1 ms through interface engineering by oxygen-terminating the diamond surface and patching it with graphene.

Carbon nanotubes are promising hosts for spin qubits, however existing demonstrations show limited coherence times. Here the authors report quantum states in a carbon-nanotube-based circuit driven solely by cavity photons and exhibiting a coherence time of about 1.3 μs.

Cluster states are a key resource in quantum technologies, but generation of large-scale 2D cluster states faces several difficulties. Here, the authors show how to generate a 2 × n ladder-like cluster state via sequential emission of time- and frequency multiplexed photonic qubits from a transmon-based device.

Encoding quantum information in qudits instead of qubits allows for several advantages, but scalable native entangling techniques would be needed. Here, the authors show how to use light-shift gates to perform entangling operations on trapped ion systems, with a calibration overhead which is independent on the qudit dimension.

An interconnect based on a low-loss detachable cable connection between two superconducting qubit devices can be used to create elementary quantum networks of interchangeable superconducting quantum devices.

CMOS-based circuits can be integrated with silicon-based spin qubits and can be controlled at milli-kelvin temperatures, which can potentially help scale up these systems.

The ultrastrong coupling regime in circuit QED allows to observe puzzling phenomena such as multiphoton exchanges between qubits and resonators. Here, the authors use two flux qubits ultrastrongly coupled to a common LC resonator to verify an earlier prediction of avoided crossing between a single photon state and a state with both of the qubits being excited.

A four-qubit processor of three phosphorus nuclear spins and an electron spin in silicon enables the implementation of a three-qubit Grover’s search algorithm with 95% fidelity. The implementation is based on an advanced multi-qubit gate with single-qubit gate fidelities above 99.9% and two-qubit gate fidelities above 99%.

Conveyor-mode spin shuttling using a two-tone travelling-wave potential demonstrates an order of magnitude better spin coherence than bucket-brigade shuttling, achieving spin shuttling over 10 μm in under 200 ns with 99.5% fidelity in an isotopically purified Si/SiGe heterostructure.

Biased noise qubits, which can selectively suppress certain types of noise, are advantageous for quantum error correction of bosonic codes. Here the authors make an important step in this direction by demonstrating quantum control of a harmonic oscillator with a biased noise qubit.

An ultra-low-loss integrated photonic chip fabricated on a customized multilayer silicon nitride 300-mm wafer platform, coupled over fibre with high-efficiency photon number resolving detectors, is used to generate Gottesman–Kitaev–Preskill qubit states.

Defects known as two-level systems are a major source of noise for superconducting qubits. Adding a phononic crystal is now shown to extend the lifetime of these two-level systems, which could lead to improved qubit coherence.

The development of electronic flying qubits requires the ability to generate and control single-electron excitations. Here the authors demonstrate quantum coherence of ultrashort single-electron plasmonic pulses in an electronic Mach-Zehnder interferometer, revealing a non-adiabatic regime at high frequencies.

Integration of color centers in wide-band semiconductors with electronic and photonic devices is required for their applications in quantum technologies. Here the authors report electronic, optical and spin control of a single vacancy center in a 4H-SiC Schottky diode integrated with optical microstructures.

Spin defects in hexagonal boron nitride are a promising platform for nanoscale magnetometry, however inhomogeneous noise degrades performance. C.J. Patrickson et al. use continuous dynamical decoupling to mitigate this noise, and to detect phase, amplitude and frequency of MHz - GHz fields.

For architectures with local connectivity, the surface code has been the leading approach to constructing fault-tolerant logical qubits, but typically requires over 1000 physical qubits per logical qubit. Here, the authors introduce a hierarchical code that maintains the same connectivity requirements as the surface code while reducing the physical qubit overhead by up to a factor of three.

The connection between classical neural networks and Gaussian processes is a fundamental result in machine learning. It has now been shown that many quantum neural networks converge to Gaussian processes, enabling their use for regression tasks.

Despite being essential to many applications in quantum science, entanglement can be easily disrupted by decoherence. A protocol based on repetitive quantum error correction now demonstrates enhanced coherence times of entangled logical qubits.

Ramsey interferometry is widely used in quantum sensing for precise qubit frequency measurements, but its sensitivity is limited by decoherence. Hecht et al. report a new protocol for detecting qubit frequency shifts in a decohering system which has enhanced sensitivity and is applicable to existing technologies.

Nonlinear light-matter coupling has applications in quantum technologies, for instance in quantum-non-demolition measurements, but its strength is typically limited. Here the authors demonstrate near-ultrastrong nonlinear light-matter coupling in a superconducting circuit with two transmons and a quarton coupler.

Hole spin qubits benefit from large spin-orbit interaction for efficient manipulation, but this can result in qubit variability. Here the authors study anisotropies in microwave-driven singlet-triplet qubits in planar germanium, revealing two distinct operating regimes due to different quantization axes alignments.

Silicon-based spin qubits are promising candidates for a scalable quantum computer. Here the authors demonstrate the violation of Bell’s inequality in gate-defined quantum dots in silicon, marking a significant advancement that showcases the maturity of this platform.

An error detecting code running on a trapped-ion quantum computer protects expressive circuits of eight logical qubits with a high-fidelity and partially fault-tolerant implementation of a universal gate set.

Disorder has emerged as a promising tool to manipulate properties of superconducting circuits. Here the authors demonstrate the use of disordered spinodal superconductor for fluxonium qubit fabrication and reveal an interesting correlation between the material disorder and the 1/f-type flux noise.

The spin state of color centers in semiconductors can be read out by optical means, but electrical readout is desirable for device applications. Here the authors develop a method for electrical readout of single spins based on the detection of surface photo-voltage and demonstrate it for NV centers in diamond.

Efficient quantum-state readout is key to quantum technologies. Here, the authors show room-temperature photoelectrical readout of single spins in silicon carbide, with a demonstrated detection efficiency superior to the conventional optical method.

Isotope engineering can enhance spin coherence of solid-state defects, such as NV centers in diamond but progress for defects in hBN has been limited. Gong et al. report the optimization of isotopes in hBN and demonstrate improved coherence and relaxation times for the negatively charged boron vacancy centers.

Electron spin qubits in semiconductors show great promise, but fast, high-fidelity readout remains challenging. Here, by precisely engineering the ___location of two multi-donor quantum dot qubits in silicon, the authors demonstrate high-fidelity latched parity readout with reduced integration time, even at elevated temperatures.

Strong intrinsic spin–orbit interaction unlocks the potential of circuit quantum electrodynamics with hole spins in silicon, resulting in strong spin–photon coupling of 300 MHz.

Low-loss superconducting aluminium cables and on-chip impedance transformers can be used to link qubit modules and create superconducting quantum computing networks with high-fidelity intermodule state transfer.

Computational search for defect centers in semiconductors typically assumes that the defects realize the most thermodynamically stable configuration. Here the authors demonstrate, for a complex defect in silicon, that this is not always the case if the kinetics of defect formation is taken into account.

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.

Efficient protocols for comparing quantum states generated on different quantum computing platforms are becoming increasingly important. Zhu et al. demonstrate cross-platform verification using randomized measurements that allow for scaling to larger systems as compared to full quantum state tomography.

Qutrits, or quantum three-level systems, can provide advantages over qubits in certain quantum information applications, and high-fidelity single-qutrit gates have been demonstrated. Goss et al. realize high-fidelity entangling gates between two superconducting qutrits that are universal for ternary computation.

Repeated observations of quantum states inhibit coherent evolution through the Zeno effect, providing opportunities for controlling multi-qubit systems. Here the authors demonstrate that projecting joint observables of three spins in diamond creates quantum Zeno subspaces that suppress dephasing.

Practical quantum computers will require protocols to carry out computation on encrypted data, just like their classical counterparts. Here, the authors present such a protocol that allows an untrusted server to implement universal quantum gates on encrypted qubits without learning about the inputs.

Superconducting flux qubits operating as two-level systems can act as artificial atoms, and so represent a potential metamaterial building block. Macha et al.assemble 20 such qubits into a metamaterial in which the ‘atoms’ are collectively coupled to the quantized mode of a microwave photon field.

Two-dimensional arrays of trapped ion qubits are attractive platforms for quantum information processing, but rapid reloading remains a challenge. Here the authors use a continuous flux of pre-cooled neutral atoms to achieve fast loading of single ions without affecting the coherence of adjacent qubits.

Silicon vacancy centres in diamond have favourable optical properties for use in quantum information processing. Here, the authors demonstrate coherent control of silicon vacancy spins, a prerequisite for the implementation of quantum computing operations.

Paramagnetic heterometallic rings have long been considered as possible qubits within a quantum information processing system. Here, the authors employ supramolecular chemistry to fabricate multiple rings around multi-armed threads, as an important step towards generating useful qubit arrays.

All-optical coherent control schemes offer well-localized and ultrafast control of individual qubits in many-qubit systems. Here the authors report on all-optical resonant and Raman-based control of single silicon vacancies using picosecond pulses, much faster than the ground state coherence time.

The Mollow triplet, originally observed in the fluorescence spectrum of an optically excited two level system, is a signature of quantum electrodynamics. Here, the authors observe its phononic equivalent by magnetically coupling a single nitrogen-vacancy qubit to the vibrations of a silicon carbide nanowire.

Atomic defects in semiconductors, like nitrogen-vacancy centres in diamond, are promising as solid state systems for quantum computing. Here, the authors show the complete quantum control of an exciton qubit formed from an isoelectronic centre in GaAs, establishing this material as a promising alternative.