Ultralight mechanical resonators based on low-dimensional materials are well suited as exceptional transducers of minuscule forces or mass changes. However, the low dimensionality also provides a challenge to minimize resistive losses and heating. Here, we report on a novel approach that aims to combine different two-dimensional (2D) materials to tackle this challenge. We fabricated a heterostructure mechanical resonator consisting of few layers of niobium diselenide (NbSe) encapsulated by two graphene sheets. The hybrid membrane shows high quality factors up to 245,000 at low temperatures, comparable to the best few-layer graphene mechanical resonators. In contrast to few-layer graphene resonators, the device shows reduced electrical losses attributed to the lower resistivity of the NbSe layer. The peculiar low-temperature dependence of the intrinsic quality factor points to dissipation over two-level systems which in turn relax over the electronic system. Our high sensitivity readout is enabled by coupling the membrane to a superconducting cavity which allows for the integration of the hybrid mechanical resonator as a sensitive and low loss transducer in future quantum circuits.

Low-frequency 1/f γ noise is ubiquitous, even in high-end electronic devices. Recently, it was found that adsorbed O2 molecules provide the dominant contribution to flux noise in superconducting quantum interference devices. To clarify the basic principles of such adsorbate noise, we have investigated low-frequency noise, while the mobility of surface adsorbates is varied by temperature. We measured low-frequency current noise in suspended monolayer graphene Corbino samples under the influence of adsorbed Ne atoms. Owing to the extremely small intrinsic noise of suspended graphene, we could resolve a combination of 1/f γ and Lorentzian noise induced by the presence of Ne. We find that the 1/f γ noise is caused by surface diffusion of Ne atoms and by temporary formation of few-Ne-atom clusters. Our results support the idea that clustering dynamics of defects is relevant for understanding of 1/f noise in metallic systems.

Entangled microwave photons form a fundamental resource for quantum information processing and sensing with continuous variables. We use a low-loss Josephson metamaterial comprising superconducting, nonlinear, asymmetric inductive elements to generate frequency-entangled photons from vacuum fluctuations at a rate of 2 giga entangled bits per second spanning over the 4-GHz bandwidth. The device is operated as a traveling-wave parametric amplifier under Kerr-relieving biasing conditions. Furthermore, we demonstrate single-mode squeezing in such devices-3.1 ± 0.7 dB below the zero-point level at half of modulation frequency.

Entangled microwave photons form a fundamental resource for quantum information processing and sensing with continuous variables. We use a low-loss Josephson metamaterial comprising superconducting non-linear asymmetric inductive elements to generate frequency (colour) entangled photons from vacuum fluctuations at a rate of 11 mega entangled bits per second with a potential rate above gigabit per second. The device is operated as a traveling wave parametric amplifier under Kerr-relieving biasing conditions. Furthermore, we realize the first successfully demonstration of single-mode squeezing in such devices -2.4 ± 0.7 dB below the zero-point level at half of modulation frequency.

We have studied 1/f noise in critical current $$I_c$$ I c in h-BN encapsulated monolayer graphene contacted by NbTiN electrodes. The sample is close to diffusive limit and the switching supercurrent with hysteresis at Dirac point amounts to $$\simeq 5$$ ≃ 5 nA. The low frequency noise in the superconducting state is measured by tracking the variation in magnitude and phase of a reflection carrier signal $$v_{rf}$$ v rf at 600–650 MHz. We find 1/f critical current fluctuations on the order of $$\delta I_c/I_c \simeq 10^{-3}$$ δ I c / I c ≃ 10 - 3 per unit band at 1 Hz. The noise power spectrum of critical current fluctuations $$S_{I_c}$$ S I c measured near the Dirac point at large, sub-critical rf-carrier amplitudes obeys the law $$S_{I_c}/{I{_c}}^2 = a/f^{\beta }$$ S I c / I c 2 = a / f β where $$a\simeq 4\times 10^{-6}$$ a ≃ 4 × 10 - 6 and $$\beta \simeq 1$$ β ≃ 1 at $$f > 0.1$$ f > 0.1  Hz. Our results point towards significant fluctuations in $$I_c$$ I c originating from variation of the proximity induced gap in the graphene junction.