Noninvasive Electron Microscopy with Interaction-free Quantum Measurements

Electron microscopy has significantly impacted many areas of science and engineering due to its unprecedented atomic and molecular resolution. Yet, the imaging of biological and other sensitive specimens has been limited because of sample damage induced by the energetic electrons necessary for imaging. The radiation dose received by a specimen during imaging with an electron microscope operating under typical conditions is comparable to the irradiation from a ten megaton hydrogen bomb exploded about thirty meters away [1]. Despite progress in hydrated environmental chambers for viewing biological specimens in their native state [2, 3], when exposed to such energetic electrons, sensitive specimens experience substantial mass loss, modification of chemical bonding, or other structural damage [2, 4]. At first sight, one might conclude that any measurement requires physical interaction with the measured object. Yet, it has been shown that a non-transmitting object in the arm of an optical interferometer can modify the interference of a single photon in such a way that the presence of the object can be detected without interaction (i.e. energy exchange) between the photon and the object [5–9]. Such interaction-free measurements have been employed in optical microscopy with photons [10]. Nobel Laureate Dennis Gabor, who investigated several electron microscopy techniques, concluded in his famous review [11]: ”The fundamental limitation of electron interferometers...is the destruction of the object by the exploring agent, and in this respect electron interferometers appear to be neither better nor worse than other instruments.” Here, we propose and show the possibility of interaction-free measurements with electrons even in the presence of previously measured quantum decoherence rates using a scheme based on charged particle trapping techniques. Use of such interaction-free measurements with electrons might dramatically reduce sample damage in electron microscopy while achieving molecularlevel resolution. We consider two ring shaped electron guides each with radius R and vertically stacked with a separation of ∆z as shown in Fig. 1a. A potential Ueff (r, z) provides