We measure the current fluctuations emitted by a normal-metal-insulator-normal-metal tunnel junction with a very wide bandwidth, from 0.3 to 13 GHz, down to very low temperature T=35  mK. This allows us to perform the spectroscopy (i.e., measure the frequency dependence) of thermal noise (no dc bias, variable temperature) and shot noise (low temperature, variable dc voltage bias). Because of the very wide bandwidth of our measurement, we deduce the current-current correlator in the time domain. We observe the thermal decay of this correlator as well as its oscillations with a period h/eV, a direct consequence of the effect of the Pauli and Heisenberg principles in quantum electron transport.

Climate change presents an existential threat to human societies and the Earth's ecosystems more generally. Mitigation strategies naturally require solving a wide range of challenging problems in science, engineering, and economics. In this context, rapidly developing quantum technologies in computing, sensing, and communication could become useful tools to diagnose and help mitigate the effects of climate change. However, the intersection between climate and quantum sciences remains largely unexplored. This preliminary report aims to identify potential high-impact use-cases of quantum technologies for climate change with a focus on four main areas: simulating physical systems, combinatorial optimization, sensing, and energy efficiency. We hope this report provides a useful resource towards connecting the climate and quantum science communities, and to this end we identify relevant research questions and next steps.

Charge transfer in a tunnel junction is studied under dc and ac voltage bias using quantum shot noise. Under dc voltage bias $V$, spectral density of noise measured within a very large bandwidth enables to deduce the current-current correlator in the time domain by Fourier transform. This correlator exhibits regular oscillations proving that electrons try to cross the junction regularly, every $h/eV$. Using harmonic and bi-harmonic ac voltage bias, we then show that quasiparticles excitations can be transferred through the junction in a controlled way. By measuring the reduction of the excess shot noise, we are able to determine the number of electron-hole pairs surrounding the injected electrons and demonstrate that bi-harmonic voltage pulses realize an on-demand electron source with a very small admixture of electron-hole pairs.Comment: 8 pages, 8 figure

We report measurements of photon-assisted transport and noise in a tunnel junction in the regime of dynamical Coulomb blockade. We have measured both dc non-linear transport and low frequency noise in the presence of an ac excitation at frequencies up to 33 GHz. In both experiments, at very low temperatures, we observe replicas at finite voltage of the zero bias features, a phenomenon characteristic of photon emission/absorption. However, the ac voltage necessary to explain our data is notably different for transport and noise, indicating that usual theory of photon-assisted phenomena fails to account for our observations.

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