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Latest articles for New Journal of Physics

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  • Reconstruction of single-photon emission with a self-calibrated wQED device based on a transmon qubit
    We present a detailed study of a microwave single-photon source utilizing a transmon qubit asymmetrically coupled to two transmission lines: a weakly coupled drive line and a strongly coupled emission line. Our design allows for the generation of single photons in the microwave regime, which are essential for quantum communication, computing, and sensing applications. In addition to single-photon generation, the same design functions as a power sensor and enables precise measurement of the system’s attenuation. This dual functionality allows us to calibrate the noise of our amplification chain. This enables a self-calibrated architecture in which the same device acts simultaneously as the photon source and as a reference standard, eliminating the need for external tones or calibrated inputs. With this calibration we reconstruct the density matrix of the emitted photon state, for which we achieve a fidelity of 61.4% and measure a second-order correlation function of , indicating quantum nature and single-photon characteristics. These results confirm generation of single photons and demonstrate the potential of transmon qubits in advancing quantum technologies in the microwave domain.

  • Multiple ionic memories in asymmetric nanochannels revealed by mem-spectrometry
    Recently discovered nanofluidic memristors, have raised promises for the development of iontronics and neuromorphic computing with ions. Ionic memory effects are related to ion dynamics inside nanochannels, with timescales associated with the manifold physicochemical phenomena occurring at confined interfaces. Here, we explore experimentally the frequency-dependent current–voltage response of model nanochannels—namely glass nanopipettes—to investigate memory effects in ion transport. This characterisation, which we refer to as mem-spectrometry, highlights two characteristic frequencies, associated with short and long timescales of the order of 50 ms and 50 s in the present system. Whereas the former can be associated with ionic diffusion, very long timescales are difficult to explain with conventional transport phenomena. We develop a minimal model accounting for these mem-spectrometry results, pointing to surface charge regulation and ionic adsorption-desorption as possible origins for the long-term memory. Our work demonstrates the relevance of mem-spectrometry to highlight subtle ion transport properties in nanochannels, giving hereby new insights on the mechanisms governing ion transport and current rectification in charged conical nanopores.

  • Laser spectroscopy of the QED-sensitive transition in Ar ...
    We experimentally study the magnetic-dipole transition in Be-like . The wavelength of this transition is known to be sensitive to the quantum electrodynamics effect and has been measured many times by emission spectroscopy using an electron beam ion trap (EBIT). However, there is a significant discrepancy among the previously measured values. Here, we report the first experimental verification of the transition wavelength by laser spectroscopy. The present result is 594.5495(21) nm, which is in reasonable agreement ( ) with the latest value measured by emission spectroscopy by the Heidelberg EBIT group.

  • The effect of the electron’s spin magnetic moment on quantum radiation in strong electromagnetic fields
    Ultra-intense laser pulses can create sufficiently strong fields to probe quantum electrodynamics effects in a novel regime. By colliding a 60 GeV electron bunch with a laser pulse focussed to the maximum achievable intensity of 1023 W cm−2, we can reach fields much stronger than the critical Schwinger field in the electron rest frame. When the ratio of these fields we find that the hard ( GeV) radiation from the electron has a substantial contribution from spin-light. 33% more photons are produced above this energy due to spin-light, the radiation resulting from the acceleration of the electron’s intrinsic magnetic moment. This increase in high-energy photons results in 14% more positrons produced with energy above 25 GeV. Furthermore, the enhanced photon production due to spin-light results in a 46% increase in the electron recoil radiation reaction. These observable signatures provide a potential route to observing spin-light in the strongly quantum regime ( ) for the first time.

  • No-go theorem for environment-assisted invariance in non-unitary dynamics
    We elucidate the requirements for quantum operations that achieve environment-assisted invariance (envariance), a symmetry of entanglement. While envariance has traditionally been studied within the framework of local unitary operations, we extend the analysis to consider non-unitary local operations. First, we investigate the conditions imposed on operators acting on pure bipartite entanglement to attain envariance. We show that the local operations must take a direct-sum form in their Kraus operator representations, establishing decoherence-free subspaces. Furthermore, we prove that this also holds for the multipartite scenario. As an immediate consequence, we demonstrate that environment-assisted shortcuts to adiabaticity cannot be achieved through non-unitary operations. In addition, we show that the static condition of the eternal black hole in AdS/CFT is violated when the CFTs are coupled to the external baths.