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Register a new userCoherence time of over a second in a telecom-compatible quantum memory storage material
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Milo\\v{s} Ran\\v{c}i\\'c
Publication date
2016
fields
Physics
and research's language is
English
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Quantum memories for light will be essential elements in future long-range quantum communication networks. These memories operate by reversibly mapping the quantum state of light onto the quantum transitions of a material system. For networks, the quantum coherence times of these transitions must be long compared to the network transmission times, approximately 100 ms for a global communication network. Due to a lack of a suitable storage material, a quantum memory that operates in the 1550 nm optical fiber communication band with a storage time greater than 1 us has not been demonstrated. Here we describe the spin dynamics of $^{167}$Er$^{3+}:$Y$_{2}$SiO$_{5}$ in a high magnetic field and demonstrate that this material has the characteristics for a practical quantum memory in the 1550 nm communication band. We observe a hyperfine coherence time of 1.3 seconds. Further, we demonstrate efficient optical pumping of the entire ensemble into a single hyperfine state, the first such demonstration in a rare-earth system and a requirement for broadband spin-wave storage. With an absorption of 70 dB/cm at 1538 nm and $Lambda$-transitions enabling spin-wave storage, this material is the first candidate identified for an efficient, broadband quantum memory at telecommunication wavelengths.
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Nanofabricated mechanical resonators are gaining significant momentum among potential quantum technologies due to their unique design freedom and independence from naturally occurring resonances. With their functionality being widely detached from material choice, they constitute ideal tools to be used as transducers, i.e. intermediaries between different quantum systems, and as memory elements in conjunction with quantum communication and computing devices. Their capability to host ultra-long lived phonon modes is particularity attractive for non-classical information storage, both for future quantum technologies as well as for fundamental tests of physics. Here we demonstrate such a mechanical quantum memory with an energy decay time of $T_1approx2$ ms, which is controlled through an optical interface engineered to natively operate at telecom wavelengths. We further investigate the coherence of the memory, equivalent to the dephasing $T_2^*$ for qubits, which exhibits a power dependent value between 15 and 112 $mu$s. This demonstration is enabled by a novel optical scheme to create a superposition state of $rvert{0}rangle+rvert{1}rangle$ mechanical excitations, with an arbitrary ratio between the vacuum and single phonon components.
We report on an experiment that demonstrates the frequency up-conversion of telecommunication wavelength single-photon-level pulses to be resonant with a $mathrm{Pr}^{3+}$:$mathrm{Y}_2mathrm{Si}mathrm{O}_5$ crystal. We convert the telecom photons at $1570,mathrm{nm}$ to $606,mathrm{nm}$ using a periodically-poled potassium titanyl phosphate nonlinear waveguide. The maximum device efficiency (which includes all optical loss) is inferred to be $eta_{mathrm{dev}}^{mathrm{max}} = 22 pm 1,%$ (internal efficiency $eta_{mathrm{int}} = 75pm8,%$) with a signal to noise ratio exceeding 1 for single-photon-level pulses with durations of up to 560$,$ns. The converted light is then stored in the crystal using the atomic frequency comb scheme with storage and retrieval efficiencies exceeding $eta_{mathrm{AFC}} = 20,%$ for predetermined storage times of up to $5,mumathrm{s}$. The retrieved light is time delayed from the noisy conversion process allowing us to measure a signal to noise ratio exceeding 100 with telecom single-photon-level inputs. These results represent the first demonstration of single-photon-level optical storage interfaced with frequency up-conversion.
We demonstrate a dual-rail optical Raman memory inside a polarization interferometer; this enables us to store polarization-encoded information at GHz bandwidths in a room-temperature atomic ensemble. By performing full process tomography on the system we measure up to 97pm1% process fidelity for the storage and retrieval process. At longer storage times, the process fidelity remains high, despite a loss of efficiency. The fidelity is 86pm4% for 1.5 mu s storage time, which is 5,000 times the pulse duration. Hence high fidelity is combined with a large time-bandwidth product. This high performance, with an experimentally simple setup, demonstrates the suitability of the Raman memory for integration into large-scale quantum networks.
Photon-based quantum information processing promises new technologies including optical quantum computing, quantum cryptography, and distributed quantum networks. Polarization-encoded photons at telecommunication wavelengths provide a compelling platform for practical realization of these technologies. However, despite important success towards building elementary components compatible with this platform, including sources of entangled photons, efficient single photon detectors, and on-chip quantum circuits, a missing element has been atomic quantum memory that directly allows for reversible mapping of quantum states encoded in the polarization degree of a telecom-wavelength photon. Here we demonstrate the quantum storage and retrieval of polarization states of heralded single-photons at telecom-wavelength by implementing the atomic frequency comb protocol in an ensemble of erbium atoms doped into an optical fiber. Despite remaining limitations in our proof-of-principle demonstration such as small storage efficiency and storage time, our broadband light-matter interface reveals the potential for use in future quantum information processing.
Significant advances in coherence have made superconducting quantum circuits a viable platform for fault-tolerant quantum computing. To further extend capabilities, highly coherent quantum systems could act as quantum memories for these circuits. A useful quantum memory must be rapidly addressable by qubits, while maintaining superior coherence. We demonstrate a novel superconducting microwave cavity architecture that is highly robust against major sources of loss that are encountered in the engineering of circuit QED systems. The architecture allows for near-millisecond storage of quantum states in a resonator while strong coupling between the resonator and a transmon qubit enables control, encoding, and readout at MHz rates. The observed coherence times constitute an improvement of almost an order of magnitude over those of the best available superconducting qubits. Our design is an ideal platform for studying coherent quantum optics and marks an important step towards hardware-efficient quantum computing with Josephson junction-based quantum circuits.
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