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Tunneling time probed by quantum shot noise

The time that a particle takes to traverse an electronic junction by tunneling has been discussed in theory [1] but not detected directly. Here, we take advantage of both optical information and electronic fluctuations from a tunneling event to estimate this traversal time at around 1.1 femtosecond. Measuring this traversal time requires current measurements at optical frequencies and remains challenging. However, it has been known for more than 40 years that as soon as the bias voltage exceeds one volt, the junction emits infrared radiation as an electrically driven optical antenna [2]. We demonstrate here that the photon emission results from the fluctuations of the current inside the tunneling barrier. Photon detection is then equivalent to a measurement of the current fluctuations at optical frequencies, allowing to probe the tunneling time. Based on this idea, we perform optical spectroscopy and electronic current fluctuation measurements in the far from equilibrium regime. Our experimental data are in very good agreement with theoretical predictions based on the Landauer-Büttiker scattering formalism. By combining the optics and the electronics, we directly estimate the so-called traversal time.

[1] R. Landauer & T. Martin. Barrier interaction time in tunneling. Review of Modern Physics 66, 217 (1994).
[2] J. Lambe & S. L. McCarthy. Light emission from inelastic electron tunneling. Physical Review Letters 37, 923 (1976).

a- Schematic of the experimental setup. The blue arrows indicate the conventional direction of the current. The red curve corresponds to the amplitude of the electric field of the SPP mode. The red arrows depict the propagating rays in the Kretschmann configuration. b- Optical picture of the Kretschmann configuration used to couple the surface plasmon polariton localized at the interface electrode/vacuum to the radiating field. The conical prism enables to collect photons via a total internal reflection ((Scale bar : 1 mm). c- Optical micrograph of the metallic cross-junction (scale bar : 100 μm). d-Emitted light from the tunnel junction (I= 1.7 mA) directly observed with a sensitive camera in the spectral range 0.4–1 μm (scale bar : 1mm).


Tunneling time probed by quantum shot noise
P. Février & J. Gabelli
Nature Communications, 9, 4940 (2018)


Julien Gabelli