We have extracted the phase coherence time τ φ of electronic quasiparticles from the low field magnetoresistance of weakly disordered wires made of silver, copper and gold. In samples fabricated using our purest silver and gold sources, τ φ increases as T −2/3 when the temperature T is reduced, as predicted by the theory of electron-electron interactions in diffusive wires. In contrast, samples made of a silver source material of lesser purity or of copper exhibit an apparent saturation of τ φ starting between 0.1 and 1 K down to our base temperature of 40 mK. By implanting manganese impurities in silver wires, we show that even a minute concentration of magnetic impurities having a small Kondo temperature can lead to a quasi saturation of τ φ over a broad temperature range, while the resistance increase expected from the Kondo effect remains hidden by a large background. We also measured the conductance of Aharonov-Bohm rings fabricated using a very pure copper source and found that the amplitude of the h/e conductance oscillations increases strongly with magnetic field. This set of experiments suggests that the frequently observed "saturation" of τ φ in weakly disordered metallic thin films can be attributed to spin-flip scattering from extremely dilute magnetic impurities, at a level undetectable by other means. I. MOTIVATIONSThe time τ φ during which the quantum coherence of an electron is maintained is of fundamental importance in mesoscopic physics. The observability of many phenomena specific to this field relies on a long enough phase coherence time. 1 Amongst these are the weak localization correction to the conductance (WL), the universal conductance fluctuations (UCF), the Aharonov-Bohm (AB) effect, persistent currents in rings, the proximity effect near the interface between a superconductor and a normal metal, and others. Hence it is crucial to find out what mechanisms limit the quantum coherence of electrons.In metallic thin films, at low temperature, electrons experience mostly elastic collisions from sample boundaries, defects of the ion lattice and static impurities in the metal. These collisions do not destroy the quantum coherence of electrons. Instead they can be pictured as resulting from a static potential on which the diffusivelike electronic quantum states are built.What limits the quantum coherence of electrons are inelastic collisions. These are collisions with other electrons through the screened Coulomb interaction, with phonons, and also with extrinsic sources such as magnetic impurities or two level systems in the metal. Whereas above about 1 K electron-phonon interactions are known to be the dominant source of decoherence, 2 electron-electron interactions are expected to be the leading inelastic process at lower temperatures in samples without extrinsic sources of decoherence. 3 The theory of electron-electron interactions in the diffusive regime was worked out in the early 1980's (for a review see 4 ). It predicts a power law divergence of τ φ when the temperature T goes to zero....

Quantum physics predicts that there is a fundamental maximum heat conductance across a single transport channel, and that this thermal conductance quantum G Q is universal, independent of the type of particles carrying the heat. Such universality, combined with the relationship between heat and information, signals a general limit on information transfer. We report on the quantitative measurement of the quantum limited heat flow for Fermi particles across a single electronic channel, using noise thermometry. The demonstrated agreement with the predicted G Q establishes experimentally this basic building block of quantum thermal transport. The achieved accuracy of below 10% opens access to many experiments involving the quantum manipulation of heat.The transport of electricity and heat in reduced dimensions and at low temperatures is subject to the laws of quantum physics. The Landauer formulation of this problem [1][2][3] introduces the concept of transport channels: a quantum conductor is described as a particle waveguide, and the channels can be viewed as the quantized transverse modes. Quantum physics sets a fundamental limit to the maximum electrical conduction across a single electronic channel. The electrical conductance quantum G e = e 2 h, where e is the unit charge and h is the Planck constant, was initially revealed in ballistic 1D constrictions [4,5]. However, different values of the maximum electrical conductance are observed for different types of charge carrying particles. In contrast, for heat conduction the equivalent thermal conductance quantumT (which sets the maximum thermal conduction across a single transport channel, k B being the Boltzmann constant, T the temperature) is predicted to be independent of the heat carrier statistics, from bosons to fermions including the intermediate 'anyons' [6][7][8][9][10][11][12][13][14][15][16]. In electronic channels, which carry both an electrical and thermal current, the pre-2 )T between G Q and G e verifies and extends the Wiedemann-Franz relation down to a single channel [8,9]. In general, the universality of G Q , together with the deep relationship between heat, entropy and information [17], points to a quantum limit on the flow of information through any individual channel [6,15]. The thermal conductance quantum has been measured for bosons, in systems with as few as 16 phonon channels [18,19], and probed at the single photon channel level [20,21]. For fermions, heat conduction was shown to be proportional to the number of ballistic electrical channels [22,23]. In [22] the data were found compatible, within an order of magnitude estimate, to the predicted thermal conductance quantum, whereas [23] demonstrated more clearly the quantization of thermal transport, but G Q was not accessible by construction of the experiment.We have measured the quantum limited heat flow across a single electronic channel using the conceptually simple approach depicted in Fig. 1A. A micron-sized metal plate is electrically connected by an adjustable number n of ballist...