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More than a century after it took the first steps, quantum mechanics is now living a second youth, mainly due to the growing efforts in exploiting inherently quantum advantages for technological applications. At the same time, more fundamentally-oriented research is still storming the citadel of quantum weirdness and paradoxes. In this page, we highlight research papers in quantum-related areas.
Interfacing single-photon emitters (SPEs) with high-finesse cavities can prevent decoherence processes, especially at elevated temperature, but its implementation remains challenging. Here, the authors report room-temperature strong coupling of SPEs in hexagonal boron nitride with a dielectric cavity based on bound states in the continuum, showing a Rabi splitting of ~ 4 meV.
Previous research reported enhanced emission from spin defects in hBN by coupling to optical resonators; however, this approach has limited scalability. Here the authors use a monolithic metasurface featuring quasi bound states fabricated from hBN to enhance photoemission and optical spin-readout efficiency of defects in the same material.
Graphene quantum dots promise applications for spin and valley qubits; however a demonstration of phase coherent oscillations has been lacking. Here the authors report coherent charge oscillations and measurements of coherence times in highly tuneable double quantum dots in bilayer graphene.
Removing excess energy (cooling) and reducing noise in superconducting quantum circuits is central to improved coherence. Lucas et al. demonstrate cooling of a superconducting resonator and its noisy environment to sub-mK temperatures by immersion in liquid 3He.
The extent of problems in quantum chemistry for which quantum algorithms could provide a speedup is still unclear, as well as the kind of speedup one should expect. Here, the authors look at the problem of ground state energy estimation, and gather theoretical and numerical evidence for the fact that an exponential quantum advantage is unlikely for generic problems of interest.
Comparing the capabilities of different quantum machine learning protocols is difficult. Here, the authors show that different learning models based on parametrized quantum circuits can all be seen as quantum linear models, thus driving general conclusions on their resource requirements and capabilities.
A possible route to scalability of trapped-ion-based quantum computing platforms is to connect multiple modules where ions can be shuttled across different registers. Here, the authors demonstrate fast and low-loss transfer of trapped ions between two microchip modules.
Fusion gates are common operations in photonic quantum information platforms, where they are employed to create entanglement. Here, the authors propose a quantum computation scheme where the same measurements used to generate entanglement can also be used to achieve fault-tolerance leading to an increased tolerance to errors.
Light interaction with atoms depends on the strength of the light-matter coupling and the energy splitting of the modes involved. Here the authors study of quantum Rabi dynamics in a deep strong coupling regime by using a cloud of cold rubidium atoms.
Quantum sensors based on NV centers in diamond are well established, however the sensitivity of detection of high-frequency radio signals has been limited. Here the authors use nanoscale field-focusing to enhance sensitivity and demonstrate ranging for GHz radio signals in an interferometer set-up.
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.
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.
Quantum sensors based on NV centers in diamond find applications in high spatial resolution NMR spectroscopy, but their operation is typically limited to low fields. Sahin et al. demonstrate a high-field sensor based on nuclear spins in diamond, where NV centers play a supporting role in optical initialization.
In large qubit registers, long coherence times and individual qubit control are difficult to achieve at the same time. Here, the authors assemble a 2D register of qubits in an array of fermionic alkaline-earth atoms, where tailored pulses can be applied to subsets of individual qubits in parallel.
The analysis of correlations in quantum networks is a difficult problem in the general case, and have so far been limited to small examples. Here, the authors show how to use symmetries and the inflation technique to derive general network entanglement criteria and certification methods.
When trying to characterise a bath coupled to a sensor qubit, one should consider that quantum environments change their properties in response to external perturbations. Here, the authors show how back-action of the qubit on the bath leads to a quench, which can be used to infer the bath spectral function.
So far, experimental results have favoured the often unstated assumption that quantum statistical properties of multiparticle systems are preserved in plasmonic platforms. Here, the authors show how multiparticle interference in photon-plasmon scattering can modify the excitation mode of plasmonic systems.
Current hypotheses towards quantisation of gravity imply the presence of a minimal length scale, which may have a role in explaining quantum-to-classical transition. Here, the authors show how assuming the minimal length scale to be a fluctuating quantity leads to a possible universal decoherence mechanism.
The way quantum simulation algorithms are translated into specific hardware implementations often translates into additional overhead. Here, the authors improve the efficiency of Hamiltonian simulation using a method that allows efficient synthesis of multi-qubit evolutions from two-qubit interactions.
Spin defects in two-dimensional materials potentially offer unique advantages for quantum sensing in terms of sensitivity and functionality. Here, the authors demonstrate the use of spin defects in hexagonal boron nitride as sensors of magnetic field, temperature and pressure, and show that their performance is comparable or exceeds that of existing platforms.
Tensor network simulations of lattice gauge theories may overcome the limitations of the Monte Carlo approach, but results have been limited to 1+1 and 2+1 dimensions so far. Here, the authors report a tree-tensor-based numerical study of a 3+1d truncated U(1) lattice gauge theory with fermionic matter.
The surface code is a keystone in quantum error correction, but it does not generally perform well against structured noise and suffers from large overheads. Here, the authors demonstrate that a variant of it has better performance and requires fewer resources, without additional hardware demands.
Background radiation has been identified as a key factor limiting the coherence times of superconducting circuits. Here, the authors measure the impact of environmental and cosmic radiation on a superconducting resonator with varying degrees of shielding, including an underground facility.
Expectations for quantum machine learning are high, but there is currently a lack of rigorous results on which scenarios would actually exhibit a quantum advantage. Here, the authors show how to tell, for a given dataset, whether a quantum model would give any prediction advantage over a classical one.
Wave-particle duality and delayed choice are keys to our understanding of quantum mechanics. Here, leveraging the capabilities of silicon nanophotonics, the authors probe the extension of wave-particle duality from dual-path to multipath case.
Information transfer between distant qubits suffers from spurious interactions and disorder. Here, the authors report up to an order of magnitude enhancement in the quality factor of a swap operation of eigenstates in a quantum dot chain, by using a periodic driving protocol inspired by discrete time crystals.
Irreversibility in quantum measurements shares conceptual links with statistical and thermodynamical irreversibility. Here, the authors are able to operationally associate an "arrow of time” to quantum weak measurements, testing it experimentally on a cloud of ultracold atoms.
Most demonstrations of quantum advantages with optics rely on single photons, and are thus difficult to scale up. Here, the authors use coherent states to demonstrate a quantum advantage for the task of verifying the solution to a NP-complete problem when only partial information on the solution is available.
The Gibbs paradox stems from the entropy change upon mixing two gases. Here, by considering bosonic and fermionic statistics, the authors show that an observer unable to distinguish the particles’ spins assigns a greater entropy increase to the mixing process than is possible in classical physics.
The quantum marginal problem interrogates the existence of a global pure quantum state with some given marginals. Here, the authors reformulate it as an optimisation problem, and specifically as the existence of a two-party separable state with additional semidefinite constraints.
Experimental demonstration of quantum speedup that scales with the system size is the goal of near-term quantum computing. Here, the authors demonstrate such scaling advantage for a D-Wave quantum annealer over analogous classical algorithms in simulations of frustrated quantum magnets.