Speaker
Description
The non-classical properties of quantum light are central to the advancement of high-precision measurement technologies. A prime example is the implementation of squeezed states for the detection of gravitational waves, a process that relies on detecting spatial modulations several orders of magnitude below the wavelength of the employed lasers [1]. In a similar vein, the so-called NOON states, a maximally entangled superposition of number states, provide an alternative route to realizing measurements that display both super-resolution and super-sensitivity, with potential applications in quantum metrology, computing, and lithography [2]. Because the metrological enhancements provided by NOON states scale directly with the number of photons N in the entangled state, maximizing this value is highly desirable. However, generating photonic NOON states with high N at high rates remains a challenge [3]. On a related note, free electrons have emerged in recent years as a promising tool for generating quantum states of light, due to their nature as sources of broadband evanescent fields that allows them to couple to strongly confined modes inside cavities and waveguides [4].
In this work, we theoretically demonstrate that free electrons can be used to generate and detect high-number photon states far beyond the reach of exclusively photonic platforms, and that an unprecedented level of sensitivity and resolution can be achieved by measuring the free-electron currents after suitably designed electron–light interaction events [5]. The key enabling mechanism is the strong electron–light coupling achieved by aloof electron reflection on an optical waveguide, leading to the emission or absorption of a high number of guided photons by each individual electron, under experimentally attainable conditions [6]. We theoretically show that combining electron-beam splitters with two electron–waveguide interactions enables a tenfold enhancement in sensitivity to optical phase shifts correlated with the average number of photons generated during the interactions, making the system robust against photon number fluctuations. Moreover, we demonstrate that waveguided NOON states containing tens of photons can be generated at megahertz rates via post-selection of the electron energy after interaction. Our work presents a novel way to exploit the quantum nature of free electrons and light to perform high-precision measurements and generate exotic states of light.
References
[1] B. P. Abbot et al. Observation of Gravitational Waves from a Binary Black Hole Merger, Phys. Rev. Lett., Vol. 116, No. 6, 061102 (2016).
[2] J. P. Dowling, Quantum optical metrology – the lowdown on high-N00N states. Contemp. Phys., Vol. 49, No. 2, 125–143 (2009).
[3] I. Afek et al. High-NOON States by Mixing Quantum and Classical Light. Science, Vol. 328, 879-881 (2010).
[4] V. Di Giulio, and F.J. García de Abajo. Optical-cavity mode squeezing by free electrons, Nanophotonics, Vol. 11, No. 21, 4659-4670 (2022).
[5] C. I. Velasco and F. J. García de Abajo, Quantum sensing and metrology with free electrons, Nat. Commun. 17, 868 (2026).
[6] L. Prelat, S. Abdullah, C. I. Velasco and F. J. García de Abajo, Unity-order coupling between free electrons and multiphoton waveguided Fock states, arXiv:2605.28383v1 (2026).