Quantum fluctuations and the single-junction Coulomb blockade

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 {ital Z}({omega}). The quantized oscillation modes of the transmission line are suddenly displaced when an electron tunnels through the junction. For small {ital 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 {ital Z}, the full blockade is recovered. Comparison with recent experiments is made.