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Adaptive femtosecond pulse shaping in an evolutionary learning loop is applied to a bioinspired dyad molecule that closely mimics the early-time photophysics of the light-harvesting complex 2 (LH2) photosynthetic antenna complex. Control over the branching ratio between the two competing pathways for energy flow, internal conversion (IC) and energy transfer (ET), is realized. We show that by pulse shaping it is possible to increase independently the relative yield of both channels, ET and IC. The optimization results are analyzed by using Fourier analysis, which gives direct insight to the mechanism featuring quantum interference of a low-frequency mode. The results from the closed-loop experiments are repeatable and robust and demonstrate the power of coherent control experiments as a spectroscopic tool (i.e., quantum-control spectroscopy) capable of revealing functionally relevant molecular properties that are hidden from conventional techniques. coherent control ͉ energy transfer ͉ quantum-control spectroscopy ͉ artificial photosynthesis A rtificial photosynthesis is an important challenge of science and technology today. Numerous applications include solar cells and other artificial power sources, light-emitting materials, sensor systems, and other electronic and photonic nanodevices that use the conversion of light energy into chemical potentials (1). Over the last decade, major technological advances have been made by using biomimicry, an approach that makes use of teachings from studies on nature's wide-ranging selection of highly efficient pigment-protein complexes (2). It has been shown that integrating light-harvesting antennae with electrontransfer relay systems is a potent way to emulate photosynthesis (3). Thus, biomimicry has inspired systems based on complicated natural light-harvesting complexes (LHCs) reduced to their basic elements, and efficient antenna systems based on polymer polyenes covalently attached to tetrapyrroles have been synthesized (4, 5).The antennae are responsible for the first step of photosynthesis, capturing energy of the sun and transferring it to subsequent photosynthetic structures where the energy is transformed in chemical potential. Within various natural and synthetic LHCs, blue-green photons are absorbed by carotenoid molecules, from which the energy is transferred to neighboring porphyrin molecules (6). This energy transfer (ET) step from the carotenoid donor to the accepting molecular species is the primary process in using energy in the 450-to 550-nm window and contributes significantly to the functioning of the complex. The efficiency of ET over competing loss processes, such as internal conversion (IC), is a crucial factor in the overall quantum yield of (artificial) photosynthesis. Hence, a high priority is given to understanding the mechanisms of energy flow and mediating processes to allow development of more efficient artificial systems.In this study, we use adaptive femtosecond pulse shaping in a learning loop (7, 8) to control the pathways of energy flow i...

We report on the realization and verification of quantum entanglement between an NV electron spin qubit and a telecom-band photonic qubit. First we generate entanglement between the spin qubit and a 637 nm photonic time-bin qubit, followed by photonic quantum frequency conversion that transfers the entanglement to a 1588 nm photon. We characterize the resulting state by correlation measurements in different bases and find a lower bound to the Bell state fidelity of ≥ 0.77 ± 0.03. This result presents an important step towards extending quantum networks via optical fiber infrastructure.Quantum networks connecting and entangling longlived qubits via photonic channels [1] may enable new experiments in quantum science as well as a range of applications such as secure information exchange between multiple nodes, distributed quantum computing, clock synchronization, and quantum sensor networks [2][3][4][5][6][7][8][9][10]. A key building block for long-distance entanglement distribution via optical fibers is the generation of entanglement between a long-lived qubit and a photonic telecomwavelength qubit (see Fig. 1a). Such building blocks are now actively explored for various qubit platforms [11][12][13][14][15][16].The NV center in diamond is a promising candidate to act as a node in such quantum networks thanks to a combination of long spin coherence and spin-selective optical transitions that allow for high fidelity initialization and single-shot read out [17]. Moreover, memory qubits are provided in the form of surrounding carbon-13 nuclear spins. These have been employed for demonstrations of quantum error correction [18][19][20] and entanglement distillation [21]. Heralded entanglement between separate NV center spin qubits has been achieved by generating spin-photon entangled states followed by a joint measurement on the photons [22].Extending such entanglement distribution over long distances is severely hindered by photon loss in the fibers. The wavelength at which the NV center emits resonant photons, the so-called zero-phonon-line (ZPL) at 637 nm, exhibits high attenuation in optical glass fibers. Quantum-coherent frequency conversion to the telecom band can mitigate these losses by roughly 7 orders of magnitude for a distance of 10 km [23,24] and would enable the quantum network to optimally benefit from the existing telecom fiber infrastructure. Recently, we have realized the conversion of 637 nm NV photons to * These two authors contributed equally to this work. † R.Hanson@tudelft.nl 1588 nm (in the telecom L-band) using a difference frequency generation (DFG) process and shown that the intrinsic single-photon character is maintained during this process [25]. However, for entanglement distribution an additional critical requirement is that the quantum information encoded by the photon is preserved during the frequency conversion.Here we demonstrate entanglement between an NV center spin qubit and a time-bin encoded frequencyconverted photonic qubit at telecom wavelength. The concept of our experiment is d...