Signatures of the Unruh Effect from Electrons Accelerated by Ultrastrong Laser Fields

We calculate the radiation resulting from the Unruh effect for strongly accelerated electrons and show that the photons are created in pairs whose polarizations are perfectly correlated. Apart from the photon statistics, this quantum radiation can further be discriminated from the classical (Larmor) radiation via the different spectral and angular distributions. The signatures of the Unruh effect become significant if the external electromagnetic field accelerating the electrons is not too far below the Schwinger limit and might be observable with future facilities. Finally, the corrections due to the birefringent nature of the QED vacuum at such ultrahigh fields are discussed.

Figure 1

Two-photon amplitudes for quantum (Unruh, left image) and classical (Larmor, right image) radiation generated by an electron which is (after being initially at rest) accelerated by a Gaussian electric field pulse with a width of 0.3 as to a moderately relativistic velocity ${\gamma }_{\max }\approx 2$ and moves to the right. The amplitudes are shown for $\mathit{k}={\mathit{k}}^{\prime }$ and $\lambda ={\lambda }^{\prime }$ and plotted as a function of $\mathit{k}$. The points in the middle of the images correspond to $\mathit{k}=0$ and the maximum $k$ values at the left and right boundaries to 30 keV. The color coding (same in both images) is chosen such that red indicates large amplitude and blue vanishing amplitude. The black areas are the excised singularities at $\mathit{k}=0$ and the black lines are isolines. One can clearly see that quantum radiation (left image) dominates inside a small forward and backward cone.