We propose a method to perform single-shot optical readout of a quantum bit (qubit) using cavity quantum electrodynamics. We selectively couple the optical transitions associated with different qubit basis states to the cavity and utilize the change in cavity transmissivity to generate a qubit readout signal composed of many photons. We show that this approach enables single-shot optical readout even when the qubit does not have a good cycling transition, which is required for standard resonance fluorescence measurements. We calculate the probability that the measurement detects the correct qubit state using the example of a quantum-dot spin under various experimental conditions and demonstrate that it can exceed 0.99.
We propose a method to perform single-shot optical readout of a quantum bit (qubit) using cavity quantum electrodynamics. We selectively couple the optical transitions associated with different qubit basis states to the cavity and utilize the change in cavity transmissivity to generate a qubit readout signal composed of many photons. We show that this approach enables single-shot optical readout even when the qubit does not have a good cycling transition, which is required for standard resonance fluorescence measurements. We calculate the probability that the measurement detects the correct qubit state using the example of a quantum-dot spin under various experimental conditions and demonstrate that it can exceed 0.99.
The accuracy of optical qubit readout is fundamentally limited by the likelihood of a qubit flip induced by the optical excitation. Experiments here show that cavity quantum electrodynamics can break this limit and significantly enhance qubit readout. For a spin in a single InAs quantum dot plus a photonic-crystal cavity, selectively coupling an optical transition of the dot to the cavity mode yields spin-dependent cavity reflectivity, enabling spin readout via the reflected optical-field intensity. This work addresses a longstanding issue in solid-state quantum information processing, and is applicable to a variety of qubit systems that lack a good cycling transition for readout.
Rapid, high-fidelity single-shot readout of quantum states is a ubiquitous requirement in quantum information technologies. For emitters with a spin-preserving optical transition, spin readout can be achieved by driving the transition with a laser and detecting the emitted photons. The speed and fidelity of this approach is typically limited by low photon collection rates and measurement back-action. Here we use an open microcavity to enhance the optical readout signal from a semiconductor quantum dot spin state, largely overcoming these limitations. We achieve single-shot readout of an electron spin in only 3 nanoseconds with a fidelity of (95.2 ± 0.7)%, and observe quantum jumps using repeated single-shot measurements. Owing to the speed of our readout, errors resulting from measurement-induced back-action have minimal impact. Our work reduces the spin readout-time well below both the achievable spin relaxation and dephasing times in semiconductor quantum dots, opening up new possibilities for their use in quantum technologies.
Quantum networking is a crucial technology towards constructing large-scale distributed quantum systems. The structure of photonic link and distributed network nodes allows high-speed and high-fidelity interconnect, enabling various applications such as distributed quantum computing and sensing, as well as secure quantum communications. Optically interfaced solid-sate spins are promising candidates for building a quantum network due to their active spin-photon interfaces, compatibility, and scalability for device integration. Especially for defect spins in silicon, the platform benefits from mature silicon photonic industry, and can access to the integration techniques developed over the past decades. T center in silicon particularly holds great expectations because of the telecom-O band optical interface, ground state doublet spin manifold, and long-lived nuclear spin coherence. Their telecom spin-photon interface provides a direct link between stationary quantum memory and flying qubits that are compatible with the existing telecommunication fiber network infrastructure. This work focuses on investigating cavity quantum electrodynamics (cQED) for cavity-coupled single T centers, its applications in quantum optical control of T center optical properties, and in realizing single-shot spin state readout. The cavity enhanced light-matter interaction mitigates the caveats of T center, such as long radiative lifetime, low Debye-Waller factor, and lack of polarization selection rule for the optical transitions. In this work, by integrating single T centers with a low-loss, small mode volume silicon photonic cavity, we have achieved the Purcell enhancement for boosting the T center fluorescence rate with a factor of 6.89. We build up the theoretical framework based on the Jaynes-Cummings model and Lindblad master equation to explain experimental observations and reveal cQED parameters. The further study on the electronic spin state readout is carried out as the fast, high-fidelity single-shot readout is critical for quantum information processing. Two methods are proposed based on realistic cQED parameters: resonant fluorescence readout in the low-cooperativity regime and spin-dependent cavity-reflection readout for intermediate- and high-cooperativity regimes. Both approaches demonstrate feasibility of high-fidelity (F > 0.95) readout, particularly the reflection readout allows F > 0.99 within a short readout time of 50 μs. This work demonstrates a promising telecom spin-photon interface with high-fidelity readout based on cavity-coupled single T centers in silicon, which are promising candidates for building future large-scale quantum networks.
The spin of a charged semiconductor quantum dot (QD) coupled to an optical cavity is a promising candidate for high-fidelity spin-photon interfaces; the cavity selectively modifies the decay rates of optical transitions such that spin initialization, manipulation, and readout are all possible in a single magnetic field geometry. By performing cavity QED calculations, we show that a cavity with a single, linearly polarized mode can simultaneously support both high-fidelity optical spin initialization and readout in a single, in-plane (Voigt geometry) magnetic field. Furthermore, we demonstrate that single-mode cavities always outperform bimodal cavities in experimentally favorable driving regimes. Our analysis, when combined with established methods of control in a Voigt geometry field, provides optimal parameter regimes for high-fidelity initialization and readout, and coherent control in both cavity configurations, providing insights for the design and development of QD spin-photon interfaces as the basis of quantum network nodes and for the generation of photonic graph states. Published by the American Physical Society 2024
Quantum state transfer into a memory, state shuttling over long distances via a quantum bus, and high-fidelity readout are important tasks for quantum technology. Realizing these tasks is challenging in the presence of realistic couplings to an environment. Here, we introduce and assess protocols that can be used in cavity quantum electrodynamics to perform high-fidelity quantum state transfer and fast quantum nondemolition qubit readout through Hamiltonian engineering. We show that high-fidelity state transfer between a cavity and a single qubit can be performed, even in the limit of strong dephasing due to inhomogeneous broadening. We generalize this result to state transfer between a cavity and a logical qubit encoded in a collective mode of a large ensemble of N physical qubits. Under a decoupling sequence, we show that inhomogeneity in the ensemble couples two collective bright states to only two other collective modes, leaving the remaining single-excitation states dark. Moreover, we show that large signal-to-noise and high single-shot fidelity can be achieved in a cavity-based qubit readout, even in the weak-coupling limit. These ideas may be important for novel systems coupling single spins to a microwave cavity.
Abstract Optically-interfaced spins in the solid state are a promising platform for quantum technologies. A crucial component of these systems is high-fidelity, projective measurement of the spin state. Here, we demonstrate single-shot spin readout of a single rare earth ion qubit, Er 3+ , which is attractive for its telecom-wavelength optical transition and compatibility with silicon nanophotonic circuits. In previous work with laser-cooled atoms and ions, and solid-state defects, spin readout is accomplished using fluorescence on an optical cycling transition; however, Er 3+ and other rare earth ions generally lack strong cycling transitions. We demonstrate that modifying the electromagnetic environment around the ion can increase the strength and cyclicity of the optical transition by several orders of magnitude, enabling single-shot quantum nondemolition readout of the ion’s spin with 94.6% fidelity. We use this readout to probe coherent dynamics and relaxation of the spin.