Spin-photon interfaces (SPIs) are key devices of quantum technologies, aimed at coherently transferring quantum information between spin qubits and propagating pulses of polarized light. We study the potential of a SPI for quantum non demolition (QND) measurements of a spin state. After being initialized and scattered by the SPI, the state of a light pulse depends on the spin state. It thus plays the role of a pointer state, information being encoded in the light's temporal and polarization degrees of freedom. Building on the fully Hamiltonian resolution of the spin-light dynamics, we show that quantum superpositions of zero and single photon states outperform coherent pulses of light, producing pointer states which are more distinguishable with the same photon budget. The energetic advantage provided by quantum pulses over coherent ones is maintained when information on the spin state is extracted at the classical level by performing projective measurements on the light pulses. The proposed schemes are robust against imperfections in state of the art semi-conducting devices.
Spin-photon interfaces (SPIs) are key devices of quantum technologies, aimed at coherently transferring quantum information between spin qubits and propagating pulses of polarized light. We study the potential of a SPI for quantum non demolition (QND) measurements of a spin state. After being initialized and scattered by the SPI, the state of a light pulse depends on the spin state. It thus plays the role of a pointer state, information being encoded in the light's temporal and polarization degrees of freedom. Building on the fully Hamiltonian resolution of the spin-light dynamics, we show that quantum superpositions of zero and single photon states outperform coherent pulses of light, producing pointer states which are more distinguishable with the same photon budget. The energetic advantage provided by quantum pulses over coherent ones is maintained when information on the spin state is extracted at the classical level by performing projective measurements on the light pulses. The proposed schemes are robust against imperfections in state of the art semi-conducting devices.
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.
The demanding requirements for a controllable large scale quantum system made of only one type of physical qubit, such as photons, can lead to complex quantum computational architectures which are challenging to realise in practise. This has driven interest towards hybrid quantum systems which can combine the relative strengths of different physical qubits to vastly simplify architecture. Here we study the key building block for a hybrid spin-photon system: the spin-photon interface (SPI). The negatively charge nitrogen-vacancy centre (NV- of research attention in recent years due to the ability to optically polarise and measure its ground state electron spin. Its long electronic spin coherence times and optical readout, at room temperature, makes the NVcentre a strong candidate for demonstrating a flexible SPI. Furthermore, coherent electronic interaction with nearby long-lived 13C nuclear spins provide a powerful platform for performing multi-qubit manipulations whilst offering extremely long coherence and storage times. However, engineering strong optical interaction with NVspins has been limited by the inability to either fabricate high quality cavities on demand, or to efficiently couple NVcentres to those cavities. Here we will describe progress towards realising a useful SPI. We detail a novel approach to constructing microcavities which will allow high-fidelity fabrication and efficient coupling of NVcentres in nanodiamond through a two-photon lithography fabrication process. We will present our lithographically defined microcavities and other developments we have made towards a SPI, such as Solid Immersion Lenses (SIL’s) and Distributed Bragg Reflectors (DBR’s). Additionally, we outline progress towards coherent electronic and nuclear spin control, a key requirement of a scalable SPI. The ability to combine the high fidelity fabrication of optical cavities with coherent spin manipulation will allow the creation of a flexible SPI that can form a core component of proposed quantum technologies.
A prerequisite for the realization of quantum networks is a coherent interface between flying and stationary qubits. So far, most of these interfaces have been based on the exchange of information between photons and collective atomic excitations. A promising alternative is the development of an interface between single photons and a single atom, employing an optical cavity to achieve sufficient coupling strength. This approach has fundamental advantages, as it allows for the individual manipulation of the atomic qubit and the implementation of a heralding scheme based on quantum non-demolition (QND) measurements of the atomic state.
Spin is a fundamental property of electrons and plays an important role in information storage. For spin-based quantum information technology, preparation and read-out of the electron spin state must be spin coherent, but both the traditional preparation and read-out of the spin state are projective to up/down spin states, which do not have spin coherence. We have recently demonstrated that the polarization coherence of light can be coherently transferred to the spin coherence of electrons in a semiconductor. We have also developed a new scheme named tomographic Kerr rotation (TKR) by generalizing the traditional KR to directly read out the spin coherence of optically prepared electrons without the need for the spin dynamics, which allows the spin projection measurement in an arbitrary set of basis states. These demonstrations were performed using g-factor-controlled semiconductor quantum wells with precessing and non-precessing electrons. The developed scheme offers a tool for performing basis-independent preparation and read-out of a spin quantum state in a solid. These results encourage us to make a quantum media converter between flying photon qubits and stationary electron spin qubits in semiconductors.
Spin is a fundamental property of electrons and plays an important role in information storage. For spin-based quantum information technology, preparation and read-out of the electron spin state must be spin coherent, but both the traditional preparation and read-out of the spin state are projective to up/down spin states, which do not have spin coherence. We have recently demonstrated that the polarization coherence of light can be coherently transferred to the spin coherence of electrons in a semiconductor. We have also developed a new scheme named tomographic Kerr rotation (TKR) by generalizing the traditional KR to directly readout the spin coherence of optically prepared electrons without the need for the spin dynamics, which allows the spin projection measurement in an arbitrary set of basis states. These demonstrations were performed using g-factor-controlled semiconductor quantum wells with precessing and nonprecessing electrons. The developed scheme offers a tool for performing basis-independent preparation and read-out of a spin quantum state in a solid. These results encourage us to make a quantum media converter between flying photon qubits and stationary electron spin qubits in semiconductors.
When atoms are illuminated by an off-resonant field, the AC Stark effect will lead to phase shifts in atomic states. The phase shifts are proportional to the photon number of the off-resonant illuminating field. By measuring the atomic phase with newly developed atom-light hybrid interferometers, we can achieve quantum non-demolition measurement of the photon number of the optical field. In this paper, we analyze theoretically the performance of this QND measurement scheme by using the QND measurement criteria established by Holland et al [Phys. Rev. A 42, 2995 (1990)]. We find the quality of the QND measurement depends on the phase resolution of the atom-light hybrid interferometers. We apply this QND measurement scheme to a twin-photon state from parametric amplifier to verify the photon correlation in the twin beams. Furthermore, a sequential QND measurement procedure is analyzed for verifying the projection property of quantum measurement and for the quantum information tapping. Finally, we discuss the possibility for single-photon-number-resolving detection via QND measurement.