Frequency-encoded linear cluster states with coherent Raman photons

Abstract

Entangled multi-qubit states are an essential resource for quantum information and computation. Solid-state emitters can mediate interactions between subsequently emitted photons via their spin, thus offering a route towards generating entangled multi-photon states. However, existing schemes typically rely on the excitation-relaxation of the emitter, resulting in single photons limited by the emitter's radiative lifetime, suffering from considerable practical limitations, for self-assembled quantum dots most notably the limited spin coherence time due to Overhauser magnetic field fluctuations. We here propose an alternative approach based on a spin-Λ system that overcomes the limitations of previous proposals. Studying the example of spin-flip Raman scattering of self-assembled quantum dots in Voigt geometry, we argue that weakly driven hole spins constitute a promising platform for the practical generation of frequency-entangled photonic cluster states.

Generation of Non‐Classical Light Using Semiconductor Quantum Dots

“…Most proposals of photonic graph states are based on pulsed polarization qubits—two orthogonal polarizations of light (e.g., horizontal and vertical, right and left circularly polarized) are treated as the and states, with different pulses being treated as different qubits. However, frequency‐encoded cluster states have also been proposed …”

Coarse-graining in retrodictive quantum state tomography

“…Define p(θ) as the distribution of random phases (supported on [0, 2π)), which dictates the distribution of effective measurement operators. This distribution depends on the physical scenario: in the example of frequency-encoded cluster-state generation in the hole-spin system in [2], when the precession time is much shorter than the emission time, p(θ)≈1/(2π). In such a case, the coherences of the reconstructed state would be completely washed out by conventional QST techniques (not making use of the knowledge of the errors θ).…”

“…Assuming a similar setup is used for the Lim et al scheme [37], we arrive at a similar phase distribution. On the other hand, for the first four schemes, γ represents the decay rate of the emitter due to spontaneous emission, whereas for the Scerri et al scheme [2] (which makes use of photonscattering), 1/γ is the loosely-optimised time between Y-rotations during which the emitter probabilistically scatters a photon. For the Lindner and Rudolph scheme [1], μ was calculated using parameters which give an error rate of 0.2%, whereas for the Denning et al scheme [38], the mean was calculated based on values suggested for high Q-factor cavities.…”

“…For the latter, we expect retrodiction to significantly improve the reconstruction fidelity. Protocol w p 2 (GHz) g 1 (ns) q ( ) p m Barrett [38] 0.955 0.167 E 0.159 Scerri et al [2] 0.420 500 QU ¥…”

“…The emitted photons are entangled with the emitter in such a way that repeated resonant control of the emitter's spin state and further excitations causes the subsequent emission of a chain of photons to be generated in a linear cluster state [1][2][3]: a key resource [4] for measurement based quantum computation [5]. Such schemes rely on an external magnetic field orthogonal to the optical axis [1][2][3]. Due to the non-zero lifetime τ d of the emitter, the spin precesses at an angular frequency ω l for a random interval.…”