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Confining particles to distances below their de Broglie wavelength discretizes their motional state. This fundamental effect is observed in many physical systems, ranging from electrons confined in atoms or quantum dots 1 , 2 to ultracold atoms trapped in optical tweezers 3 , 4 . In solid-state photonics, a long-standing goal has been to achieve fully tunable quantum confinement of optically active electron–hole pairs, known as excitons. To confine excitons, existing approaches mainly rely on material modulation 5 , which suffers from poor control over the energy and position of trapping potentials. This has severely impeded the engineering of large-scale quantum photonic systems. Here we demonstrate electrically controlled quantum confinement of neutral excitons in 2D semiconductors. By combining gate-defined in-plane electric fields with inherent interactions between excitons and free charges in a lateral p–i–n junction, we achieve exciton confinement below 10 nm. Quantization of excitonic motion manifests in the measured optical response as a ladder of discrete voltage-dependent states below the continuum. Furthermore, we observe that our confining potentials lead to a strong modification of the relative wave function of excitons. Our technique provides an experimental route towards creating scalable arrays of identical single-photon sources and has wide-ranging implications for realizing strongly correlated photonic phases 6 , 7 and on-chip optical quantum information processors 8 , 9 . Electrically controlled quantum confinement of excitons to below 10 nm is achieved in a 2D semiconductor by combining in-plane electric fields with interactions between excitons and free charges.

When the Coulomb repulsion between electrons dominates over their kinetic energy, electrons in two-dimensional systems are predicted to spontaneously break continuous-translation symmetry and form a quantum crystal 1 . Efforts to observe 2 – 12 this elusive state of matter, termed a Wigner crystal, in two-dimensional extended systems have primarily focused on conductivity measurements on electrons confined to a single Landau level at high magnetic fields. Here we use optical spectroscopy to demonstrate that electrons in a monolayer semiconductor with density lower than 3 × 10 11  per centimetre squared form a Wigner crystal. The combination of a high electron effective mass and reduced dielectric screening enables us to observe electronic charge order even in the absence of a moiré potential or an external magnetic field. The interactions between a resonantly injected exciton and electrons arranged in a periodic lattice modify the exciton bandstructure so that an umklapp resonance arises in the optical reflection spectrum, heralding the presence of charge order 13 . Our findings demonstrate that charge-tunable transition metal dichalcogenide monolayers 14 enable the investigation of previously uncharted territory for many-body physics where interaction energy dominates over kinetic energy. The signature of a Wigner crystal—the analogue of a solid phase for electrons—is observed via the optical reflection spectrum in a monolayer transition metal dichalcogenide.

The interaction between a mobile quantum impurity and a bosonic bath leads to the formation of quasiparticles, termed Bose polarons. The elementary properties of Bose polarons, such as their mutual interactions, can differ drastically from those of the bare impurities. Here, we explore Bose polaron physics in a two-dimensional nonequilibrium setting by injecting \\(^-\\) polarised exciton-polariton impurities into a bath of coherent \\(^+\\) polarised polaritons generated by resonant laser excitation of monolayer MoSe\\(_2\\) embedded in an optical cavity. By exploiting a biexciton Feshbach resonance between the impurity and the bath polaritons, we tune the interacting system to the strong-coupling regime and demonstrate the coexistence of two new quasiparticle branches. Using time-resolved pump-probe measurements we observe how polaron dressing modifies the interaction between impurity polaritons. Remarkably, we find that the interactions between high-energy polaron quasiparticles, that are repulsive for small bath occupancy, can become attractive in the strong impurity-bath coupling regime. Our experiments provide the first direct measurement of Bose polaron-polaron interaction strength in any physical system and pave the way for exploration and control of many-body correlations in driven-dissipative settings.

Quantum confinement is the discretization of energy when motion of particles is restricted to length scales smaller than their de Broglie wavelength. The experimental realization of this effect has had wide ranging impact in diverse fields of physics and facilitated the development of new technologies. In semiconductor physics, quantum confinement of optically excited quasiparticles, such as excitons or trions, is typically achieved by modulation of material properties - an approach crucially limited by the lack of insitu tunability and scalability of confining potentials. Achieving fully tunable quantum confinement of optical excitations has therefore been an outstanding goal in quantum photonics. Here, we demonstrate electrically controlled quantum confinement of neutral excitons in a gate-defined monolayer p-i-n diode. A combination of dc Stark shift induced by large in-plane fields and a previously unknown confining mechanism based on repulsive interaction between excitons and free charges ensures tight exciton confinement in the narrow neutral region. Quantization of exciton motion manifests in multiple discrete, spectrally narrow, voltage-dependent optical resonances that emerge below the free exciton resonance. Our measurements reveal several unique physical features of these quantum confined excitons, including an in-plane dipolar character, one-dimensional center-of-mass confinement, and strikingly enhanced exciton size in the presence of magnetic fields. Our method provides an experimental route towards creating scalable arrays of identical single photon sources, which will constitute building blocks of strongly correlated photonic systems.

Systematic transrectal ultrasound biopsies have been the first-line biopsy strategy in men with suspected prostate cancer for over 30 years. Transperineal biopsy is an alternative approach but has been predominately reserved as a repeat biopsy strategy and not widely used as a first-line approach. This study evaluates the diagnostic and clinical outcomes of transperineal sector biopsy (TPSB) as a first-line biopsy strategy in the diagnosis and management of prostate cancer. A multi-institutional review of 402 consecutive patients who underwent primary transperineal sector biopsy. All patients had no prior history of prostate biopsy. TPSB was carried out as a day-case procedure under general or regional anaesthesia. The cancer detection rate, location and complications for all cases were evaluated. Prostate cancer was identified in 249 patients (61.9%) and was comparably sited across anterior, middle and posterior sectors. The disease was clinically significant (Gleason 3+4 or > 4mm maximum cancer length) in 187 patients (47%). Post biopsy urinary retention occurred in 6 patients (1.5%). Hematuria requiring overnight hospital admission occurred in 4 patients (1.0%). There were no cases of urosepsis. As a primary diagnostic strategy, TPSB is a safe and effective technique with high cancer detection rates. It also offers an attractive compromise to more extensive transperineal protocols, which can be more time-consuming and associated with higher morbidity. .