Quantum memories will be an essential part of many quantum information protocols, including distributed quantum computing, quantum sensing, and the synchronization of repeater nodes. Most efforts toward developing such a quantum memory have been focused on matter-based storage systems, which convert the energy and information from an optical state to an atomic state of matter to be retrieved later. These matter memories, while capable of achieving great storage times, have several limitations; namely, they are inherently narrow bandwidth, they typically do not operate at key telecommunications wavelengths, and often require costly overhead in the form of cryogenics. In this work, we have developed a quantum memory that operates in free space at room temperature, allowing us to avoid all the previously mentioned limitations, and achieve a record-high time-bandwidth product.
We present progress toward measuring nanometer-scale vibrations via a frequency-entangled two-photon interferometer. Unlike classical interference, two-photon – or Hong-Ou-Mandel – interference allows for optical metrology with resilience against imbalanced loss, dispersion, and optical background. However, the resolution of traditional degenerate frequency two-photon interference is limited by the photons’ bandwidths, requiring large bandwidths or long integration times to achieve nanometer-scale resolution. We have implemented a twophoton interferometer utilizing highly non-degenerate frequency-entangled photon pairs at 810 nm and 1550 nm, drastically increasing measurement sensitivity while retaining the advantages of two-photon interference. This enhancement comes via a beat note with frequency proportional to the photon detuning of 177 THz. The resulting measurement saturates the quantum Cram´er-Rao bound, maximizing the information extracted per photon. We have demonstrated a measurement resolution of 2.3 nm with fewer than 18,000 detected photon pairs, orders of magnitude better than previous results. By reflecting one photon from the pair off a target surface, we may use our system to study small-scale vibrations.
Photonic quantum memories will play an essential role in several quantum information protocols, including distributed quantum computing, quantum sensing, and the synchronization of repeater nodes. Most photonic memories operate by storing the photon in matter-based systems, but those approaches have limitations. Namely, they are inherently narrow bandwidth, often require costly overhead in the form of cryogenics, and typically have low retrieval efficiency into single-mode fiber. In this work, we develop a photonic quantum memory that operates at room temperature in free space, allowing us to avoid the aforementioned drawbacks.
Quantum optical memories are a key component in a variety of quantum information applications, from extending quantum communication channels to building high-efficiency single-photon sources to enabling protocols requiring multiple synchronized qubits. However, most current photon storage systems utilize light-matter interactions and are therefore not broadband; meanwhile the available broader-bandwidth photon storage systems operate with somewhat shorter storage times or require cryogenic operation. Here we develop a system with multiplexed free-space storage cavities, able to store single photons with high efficiency over variable delays, up to 12.5 µs, and over multiple nanometers bandwidth at room temperature. The system can store multiple qubits encoded in various degrees of freedom (e.g., time-bin, and polarization) simultaneously. The work presented here has demonstrated storage of polarization states for 1.25 µs and retrieval through single-mode fiber with a state fidelity >99% and efficiency 82%.
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