We investigate the effect of quantum fluctuations on the Coulomb blockade in a single tunnel junction coupled to its environment by a transmission line of arbitrary impedance Z(ω). The quantized oscillation modes of the transmission line are suddenly displaced when an electron tunnels through the junction. For small Z (relative to the quantum of resitance), a weak power-law zero-bias anomaly occurs associated with the infrared-divergent shakeup of low-frequency transmission-line modes. For large Z, the full blockade is recovered. Comparison with recent experiments is made.

• Received 29 January 1990

DOI:https://doi.org/10.1103/PhysRevLett.64.3183