Dynamical quantum field entanglement and performance of photonic gate

Shabnam Siddiqui, Julio R. Gea-Banacloche

We study the performance of an adiabatic geometric phase gate with a quantized driving field numerically and develop an analytical approximation that shows how the qubit becomes entangled with the driving field. This results in a scaling of the gate error probability versus the energy in the control field that has the same form as that found for dynamic, nonadiabatic gates, but with a prefactor that would typically be several orders of magnitude larger, because of the adiabaticity constraint. In the approximation we have used, which should be valid for sufficiently large control fields, the main source of decoherence (and hence error) is the ``which path'' information carried by the photons that would be radiated by the driven qubit.

Panagiotis Vergyris

Anton Zeilinger

Tejas Acharya, Loïc Lanco, Olivier Krebs +3 more

Light-matter interfaces are pivotal for quantum computation and communication. While typically analyzed using single-mode or open-quantum-system approximations, these models often neglect multi-mode field states and light-matter entanglement, hindering exact protocol modeling. Here, we solve the full Hamiltonian dynamics of a solid-state spin-photon interface for three key protocols: the generation of photon-number superpositions, a controlled photon-photon gate, and the production of photonic cluster states. By deriving exact fidelities, we identify fundamental performance limits. Our results reveal that while realistic imperfections severely limit photon-photon gates, they only slightly affect linear photonic clusters and are nearly harmless for photon-number state superpositions.

Bruno O. Goes

Quantum interfaces are ubiquitous in quantum technologies as they allow the implementation of several functionalities including quantum memories, quantum repeaters, photonic gates, and highly entangled photonic state generation. Based on the coherent coupling between quantum emitters and propagating pulses of light, they can be realized on a large variety of experimental platforms where quantum non-demolition measurements, entanglement generation, and efficient production of non-classical resources have been reported.This thesis explores the potential of so-called collision models to model exactly the light-matter dynamics in various kinds of quantum interfaces, providing direct access to their joint entangled states. It allows us to derive analytic expressions of the device performance, whether operated as a measuring apparatus or a source of cluster states. Since our model captures light and matter as a closed system, it verifies global energy conservation, providing access to the energy budget associated with the execution of the quantum task.Initially, we review the theoretical foundation for quantum measurements and introduce figures of merit used throughout the thesis. Subsequently, we review the collision model method, which is based on waveguide quantum electrodynamics (WGQED), setting the stage for subsequent analyses. Then, we address fundamental inquiries. First, we investigate the emergence of non-classical behavior of the field scattered by a quantum emitter that interacts with an intense resonant coherent field. It reveals signatures of quantum contextuality—negativity in the Wigner function and anomalous weak values. Second, we investigate the possibility of non-destructive spin state measurement by limiting the energy budget to at most one photon. We compare the performance of two different fields: coherent field and number state superposition. We demonstrate better performance of the latter in entanglement generation, thus providing a quantum advantage. Lastly, our analysis extends to technological applications. We propose a photon-photon gate, conduct a thorough error analysis, and we perform the modeling of cutting-edge experiments envisioning the deterministic generation of highly entangled states of light.This theoretical capacity opens the way to directly optimizing the device performance and efficiency as a function of the parameters accessible to experimentalists. It also allows us to fit experimental data with high accuracy.

Deniz Türkpençe