Quantum phase slip noise

Quantum phase slips (QPSs) generate voltage fluctuations in superconducting nanowires. Employing the Keldysh technique and making use of the phase-charge duality arguments, we develop a theory of QPS-induced voltage noise in such nanowires. We demonstrate that quantum tunneling of the magnetic flux quanta across the wire yields quantum shot noise which obeys Poisson statistics and is characterized by a power-law dependence of its spectrum $S_{\mathrm{\Omega }}$ on the external bias. In long wires, $S_{\mathrm{\Omega }}$ decreases with increasing frequency $\mathrm{\Omega }$ and vanishes beyond a threshold value of $\mathrm{\Omega }$ at $T\to 0$. The quantum coherent nature of QPS noise yields nonmonotonous dependence of $S_{\mathrm{\Omega }}$ on $T$ at small $\mathrm{\Omega }$.

Figure 1

The system under consideration. The figure also illustrates creation of two plasmons by a QPS.

Figure 2

Candylike diagrams which determine both average voltage (9) (upper diagram) and voltage noise (12) (six remaining diagrams) in the second order in ${\gamma }_{\mathrm{QPS}}$. The fields ${\phi }_{+}, {\chi }_{+}$, and ${\chi }_{-}$ in the propagators (13) are denoted, respectively by wavy, solid, and dashed lines.

Figure 3

The frequency dependence of the QPS noise spectrum $S_{\mathrm{\Omega }}$ (30) at $\lambda =2.7$, large $E_C$, and different $T$ in the long-wire limit. The inset shows $S_{\mathrm{\Omega }}$ as a function of $T$.