Efficient and low-noise distribution of photons is essential for quantum technology networks. Current strategies focus on low-loss distribution channels or the use of quantum repeaters. I will present a surprising alternate strategy: transporting photons stored in a quantum hard drive. Recent results demonstrate the potential for such a device in rare-earth ion crystals with coherence lifetimes greater than 6 hours. With a sufficiently high photonic storage capacity, quantum hard drives will enable new regimes of science, such as optical astronomy below 1 µas resolution using very long baseline interferometry.
Efficient and low-noise distribution of photons is essential for quantum technology networks. Current strategies focus on low-loss distribution channels or the use of quantum repeaters. I will present a surprising alternate strategy: transporting photons stored in a quantum hard drive. Recent results demonstrate the potential for such a device in rare-earth ion crystals with coherence lifetimes greater than 6 hours. With a sufficiently high photonic storage capacity, quantum hard drives will enable new regimes of science, such as optical astronomy below 1 µas resolution using very long baseline interferometry.
The fields of astronomy and quantum photonics are united by a need to manage very small numbers of photons. In particular, for astronomy in order to extend very long baseline interferometers to the infrared and optical, would require very low loss optical connections spanning several 100 km. It is here where the developments in quantum technologies may provide the solution. With quantum memories demonstrating coherence times of several hours, it may be possible to transport photons stored in such a memory over distances up to hundreds of kilometres, with minimal loss and infrastructure investment. This thesis seeks to explore some of the challenges that may arise when implementing such a scheme. The most critical to the implementation of an hour long lifetime quantum memory is the precise control of the magnetic field environment. This thesis makes a numerical study of locating field insensitive points, as well as an experimental study of the underlying structure for efficient searches and what regimes to target in future experiments. Transporting a quantum hard drive will also be limited by the memory’s sensitivity to the forces associated with moving it. This thesis details a scheme to measure the piezospectroscopic response of Er:Y2SiO5 finding the tensor component along the b-axis to be 35±2 kHz/kPa. This value indicates that Er:Y2SiO5 may be less susceptible to vibrations than similar rare-earth materials, and that passive vibration damping is likely sufficient. Finally, this thesis explores the problem of filtering noise photons that lie outside the spectrally narrow storage regions. Fibre Bragg grating (FBG) filters are explored, with fabricated devices achieving maximum attenuations of 127.6±0.3 dB, with less than 1 dB of insertion loss. Measurements of narrow filters with O(10 kHz) bandwidths are also discussed. Overall FBG’s have proven to be both high performance, and highly customisable indicating they are suitable for use in a QHD.
The ability of storing and retrieving quantum states of light is an important experimental challenge in quantum information science. A powerful quantum memory for light is required in a quantum repeater, which would allow long distance (>500km) quantum communications. To be implemented in such application, the quantum memory must allow on-demand readout, with high fidelity and efficiency, and a long storage time. Additionally a multimode capacity (for temporal or spatial modes) would allow multiplexing. Our approaches focus on rare-earth doped crystals, i.e. solid state quantum memory. I present, in this work, our contributions for a solid-state quantum storage, with good performances in every criteria. In particular, I present the preservation of quantum entanglement during the storage, which paves the way for the implementation of quantum memories in quantum repeaters.
Abstract Quantum memory is a core enabling device for large-scale quantum networks, serving as the fundamental building block for quantum repeaters and transportable quantum memories. Among various physical platforms, rare-earth-ion-doped crystals stand out as one of the most promising solid-state candidates for long-lived photonic quantum memories, owing to their exceptionally long spin coherence time and their compatibility with integration. In this review, we first introduce the physical mechanisms underlying long-lived spin coherence in rare-earth systems, with particular emphasis on the zero-first-order-Zeeman transition and dynamical decoupling techniques. We then review the experimental progress in this field, highlighting three distinct lifetimes—the spin coherence time, the light storage time, and the quantum storage time—and covering experiments that have achieved hour-scale spin coherence, minute- to hour-scale light storage, and minute-scale single-photon-level quantum storage. Finally, we discuss the remaining challenges that hinder the realization of practical long-lived quantum memories, explore potential strategies to overcome these obstacles, and outline the prospects for their future applications in quantum networks.
Physics
Photons are ideal carriers of information. They are fast and coherent, and because they don't interact much with each other they can have very long lifetimes. However, stopping, processing, and manipulating the photons requires them to be stored in a memory, where doing so can damage their fragile quantum properties, which leads to a loss of coherence. Although photons have been coherently stored in and retrieved from ensembles of atom gases, both warm and cold atom clouds, for practical applications a solid-state memory would be desired. Heinze et al. have developed a method to enhance the storage time of photons in a rare-earth–ion—doped crystal. They use a series of laser pulses to initialize the crystal for photon storage and then load it with their “information photons.” By iteratively optimizing the experimental parameters, they show that they can store light pulses and even entire images in the crystal and then retrieve them up to a minute later with their coherent properties intact. The results present an important step toward building a viable quantum network.
Phys. Rev. Lett. 111 , 033601(2013).
Optical quantum networks for distributing entanglement between quantum machines will enable distributed quantum computing, secure communications and new sensing methods. These networks will contain quantum transducers for connecting computing qubits to travelling optical photon qubits, and quantum repeater links for distributing entanglement at long distances. In this talk I present implementations of quantum hardware for repeaters and transducers using nano-photonics and rare-earth ions, like ytterbium and erbium, exhibiting highly coherent optical and spin transitions in a solid-state environment. In particular, i discuss optically addressable single quantum bits with single shot readout based on ytterbium 171 atoms, and on-chip storage and processing of photons using erbium ensembles coupled to silicon photonics.
Due to the inevitable loss of single photon transmission in optical fiber, a quantum repeater scheme is needed to establish large-scale quantum networks. The existing elementary quantum repeater links are all based on emissive quantum memories, with entangled photons emitted by the memory itself. This architecture is difficult to support deterministic photon emission and multiplexing storage simultaneously, which fundamentally limits the rate of entanglement distribution. In this talk, I will present our recent work about the realization of heralded quantum entanglement between two absorptive quantum memories based on rare-earth-ion-doped crystals. This work confirmed the feasibility of constructing quantum repeater based on absorptive quantum memories and demonstrated the acceleration effect of multiplexing in quantum repeater for the first time, which lays a solid foundation for the construction of practical high-speed quantum networks.