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Long-range quantum communication requires the development of in-out light-matter interfaces to achieve a quantum advantage in entanglement distribution. Ideally, these quantum interconnections should be as fast as possible to achieve high-rate entangled qubits distribution. Here, we demonstrate the coherent quanta exchange between single photons generated on-demand from a GaAs quantum dot and atomic ensemble in a $^{87}$Rb vapor quantum memory. Through an open quantum system analysis, we demonstrate the mapping between the quantized electric field of photons and the coherence of the atomic ensemble. Our results play a pivotal role in understanding quantum light-matter interactions at the short time scales required to build fast hybrid quantum networks., Comment: arXiv admin note: text overlap with arXiv:1808.05921; v2: figure typo corrected

The generation of entangled photon pairs which are compatible with quantum devices and standard telecommunication channels are critical for the development of long range fiber quantum networks. Aside from wavelength, bandwidth matching and high fidelity of produced pairs are necessary for high interfacing efficiency. High-rate, robust entanglement sources that satisfy all these conditions remain an outstanding experimental challenge. In this work, we study an entanglement source based on four-wave mixing in a diamond configuration in a warm rubidium vapor. We theoretically and experimentally investigate a new operating regime and demonstrate an entanglement source which produces highly non-degenerate $795$ and $1324$-nm photon pairs. With this source we are able to achieve in-fiber entangled pair generation rates greater than $10^7\, /s$, orders of magnitude higher than previously reported atomic sources. Additionally, given our source's native compatibility with telecom infrastructure and atomic systems, it is an important step towards scalable quantum networks.

First-generation long-distance quantum repeater networks require quantum memories capable of interfacing with telecom photons to perform quantum-interference-mediated entanglement generation operations. The ability to demonstrate these interconnections using real-life fiber connections in a long-distance setting is paramount to realize a scalable quantum internet. Here we address these significant challenges by observing Hong-Ou-Mandel (HOM) interference between indistinguishable telecom photons produced in two independent room temperature quantum memories, separated by a distance of 158 km. We obtained interference visibilities after long-distance propagation of $\rm \boldsymbol{V=(38\pm2)\%}$ for single-photon level experimental inputs. This first-of-its-kind quantum network prototype connecting quantum laboratories in Stony Brook University and Brookhaven National Laboratory is envisioned to evolve into a large-scale memory-assisted entanglement distribution quantum network, the basis for inter-city quantum communication., 17 pages, 11 figures

Long range quantum communication and quantum information processing require the development of light-matter interfaces for distributed quantum networks. Even though photons are ideal candidates for network links to transfer quantum information, the system of choice for the realization of quantum nodes has not been identified yet. Ideally, one strives for a hybrid network architecture, which will consist of different quantum systems, combining the strengths of each system. However, interfacing different quantum systems via photonic channels remains a major challenge because a detailed understanding of the underlying light-matter interaction is missing. Here, we show the coherent manipulation of single photons generated on-demand from a semiconductor quantum dot using a rubidium vapor quantum memory, forming a hybrid quantum network. We demonstrate the engineering of the photons' temporal wave function using four-level atoms and the creation of a new type of electromagnetic induced transparency for quantum dot photons on resonance with rubidium transitions. Given the short lifetime of our quantum dot transition the observed dynamics cannot be explained in the established steady-state picture. Our results play a pivotal role in understanding quantum light-matter interactions at short time scales. These findings demonstrate a fundamental active node to construct future large-scale hybrid quantum networks., 16 pages, 5 figures

First generation quantum repeater networks require independent quantum memories capable of storing and retrieving indistinguishable photons to perform quantum-interference-mediated high-repetition entanglement swapping operations. The ability to perform these coherent operations at room temperature is of prime importance in order to realize large scalable quantum networks. Here we address these significant challenges by observing Hong-Ou-Mandel (HOM) interference between indistinguishable photons carrying polarization qubits retrieved from two independent room-temperature quantum memories. Our elementary quantum network configuration includes: (i) two independent sources generating polarization-encoded qubits; (ii) two atomic-vapor dual-rail quantum memories; and (iii) a HOM interference node. We obtained interference visibilities after quantum memory retrieval of $\rm \boldsymbol{V=(41.9\pm2.0)\%}$ for few-photon level inputs and $\rm \boldsymbol{V=(25.9\pm2.5)\%}$ for single-photon level inputs. Our prototype network lays the groundwork for future large-scale memory-assisted quantum cryptography and distributed quantum networks., Comment: 12 pages, 6 figures

The development of useful photon-photon interactions can trigger numerous breakthroughs in quantum information science, however this has remained a considerable challenge spanning several decades. Here we demonstrate the first room-temperature implementation of large phase shifts ($\approx��$) on a single-photon level probe pulse (1.5us) triggered by a simultaneously-propagating few-photon-level signal field. This process is mediated by $Rb^{87}$ vapor in a double-$��$ atomic configuration. We use homodyne tomography to obtain the quadrature statistics of the phase-shifted quantum fields and perform maximum-likelihood estimation to reconstruct their quantum state in the Fock state basis. For the probe field, we have observed input-output fidelities higher than 90$\%$ for phase-shifted output states, and high overlap (over 90\%) with a theoretically perfect coherent state. Our noise-free, four-wave-mixing-mediated photon-photon interface is a key milestone towards developing quantum logic and nondemolition photon detection using schemes such as coherent photon conversion., 10 pages, 6 figures

Here we use a slow light quantum light-matter interface at room temperature to implement an analog simulator of complex relativistic and topological physics. We have realized the famous Jackiw-Rebbi model (JR), the celebrated first example where relativity meets topology. Our system is based upon interacting dark state polaritons (DSP's) created by storing light in a rubidium vapor using a dual-tripod atomic system. The DSP's temporal evolution emulates the physics of Dirac spinors and is engineered to follow the JR regime by using a linear magnetic field gradient. We also probe the obtained topologically protected zero-energy mode by analyzing the time correlations between the spinor components. Our implementation paves the way towards quantum simulation of more complex phenomena involving many quantum relativistic particles., 7 pages, 4 figures

The ability to interface multiple optical quantum devices is a key milestone towards the development of future quantum networks that are capable of sharing and processing quantum information encoded in light. One of the requirements for any node of these quantum networks will be cascadability, i.e. the ability to drive the input of a node using the output of another node. Here, we report the cascading of quantum light-matter interfaces by storing few-photon level pulses of light in warm vapor followed by the subsequent storage of the retrieved field onto a second ensemble. We demonstrate that even after the sequential storage, the final signal-to-background ratio can remain greater than 1 for weak pulses containing 8 input photons on average., Comment: 5 pages, 5 figures

An optical quantum memory is a stationary device that is capable of storing and recreating photonic qubits with a higher fidelity than any classical device. Thus far, these two requirements have been fulfilled in systems based on cold atoms and cryogenically cooled crystals. Here, we report a room-temperature quantum memory capable of storing arbitrary polarization qubits with a signal-to-background ratio higher than 1 and an average fidelity clearly surpassing the classical limit for weak laser pulses containing 1.6 photons on average. Our results prove that a common vapor cell can reach the low background noise levels necessary for quantum memory operation, and propels atomic-vapor systems to a level of quantum functionality akin to other quantum information processing architectures.