Master Thesis Defense by IasonTsiamis – University of Copenhagen

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Master Thesis Defense by IasonTsiamis

Continuous wave single-photon transistor with Rydberg atoms

The rapid evolution of the quantum technologies demands, the development of efficient tools - quantum gates - to control and modify quantum signals. One of the devices from this family is an optical quantum transistor, being an analog of a classical field effect transistor. Similar to its electronic counterpart, it is a device where a small optical ’control’ field is used to switch on and off the propagation of another optical ’signal’ field via a nonlinear optical interaction. The fundamental limiting case of an optical quantum transistor is a single-photon transistor, where the presence or absence of a single photon in the gate field, controls the propagation of the ’signal’ field.

In this work I develop a single photon transistor model, which consists of an ensemble of Rydberg atoms located inside a single-sided cavity, coupled to two driving fields. A ’signal’ field incident on the ensemble can be reflected or lost, conditioned by the absence or presence of a ’control’ field that is mapped to a collective Rydberg excitation, which leads to Rydberg blockade. An advantage the current proposal compared to previous models, is that driving fields are continuously turned on throughout the entire protocol, leading to the continuous wave version of the single photon transistor. This largely simplifies the protocol and possible experimental realization of the transistor. 

The scheme relies on the impedance matching condition for a signal photon, working in the presence of a probe, on the contrary of previous proposals. Namely, once we send the single-photon ’control’ signal, it can be mapped to a very long lived Rydberg excitation exploiting the dephasing processes imposed by the probing. This leads to the blockade and reflection of a coherent multiphoton field, where the number of scattered probe photons defines the gain transistor. Noteworthly, the proposed device could be used also as an efficient optical single-photon detector. In this case the protocol allows for the detection of a presence or absence of the single control field by measuring the reflected signal field . The efficient multiphoton blockade is enabled by the long lifetime of the Rydberg excitation, potentially leading to the detection with large signal-to-noise ratio.