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1. Optimal photonic gates for quantum-enhanced telescopes

   https://doi.org/10.48550/ARXIV.2108.01170  

   Czupryniak, R.; Steinmetz, J.; Kwiat, P. G.; Jordan, A. N. (October 2021, ArXivorg)

   We propose two optimal phase-estimation schemes that can be used for quantum-enhanced long-baseline interferometry. By using distributed entanglement, it is possible to eliminate the loss of stellar photons during transmission over the baselines. The first protocol is a sequence of gates using nonlinear optical elements, optimized over all possible measurement schemes to saturate the Cramér-Rao bound. The second approach builds on an existing protocol, which encodes the time of arrival of the stellar photon into a quantum memory. Our modified version reduces both the number of ancilla qubits and the number of gate operations by a factor of two. 

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2. Increasing the Raw Key Rate in Energy-Time Entanglement Based Quantum Key Distribution

   https://doi.org/10.1109/IEEECONF51394.2020.9443428  

   Karimi, Esmaeil; Soljanin, Emina; Whiting, Philip (November 2020, 2020 54th Asilomar Conference on Signals, Systems, and Computers)

   null (Ed.)

   A Quantum Key Distribution (QKD) protocol describes how two remote parties can establish a secret key by communicating over a quantum and a public classical channel that both can be accessed by an eavesdropper. QKD protocols using energy-time entangled photon pairs are of growing practical interest because of their potential to provide a higher secure key rate over long distances by carrying multiple bits per entangled photon pair. We consider a system where information can be extracted by measuring random times of a sequence of entangled photon arrivals. Our goal is to maximize the utility of each such pair. We propose a discrete-time model for the photon arrival process, and establish a theoretical bound on the number of raw bits that can be generated under this model. We first analyze a well-known simple binning encoding scheme, and show that it generates a significantly lower information rate than what is theoretically possible. We then propose three adaptive schemes that increase the number of raw bits generated per photon, and compute and compare the information rates they offer. Moreover, the effect of public channel communication on the secret key rates of the proposed schemes is investigated. 

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3. Astronomical interferometry using continuous variable quantum teleportation

   https://doi.org/10.1103/PhysRevResearch.7.023154  

   Wang, Yunkai; Zhang, Yujie; Lorenz, Virginia O (May 2025, Physical Review Research)

   We propose a method to build an astronomical interferometer using continuous-variable quantum teleportation to overcome transmission loss between distant telescopes. The scheme relies on two-mode squeezed states shared by distant telescopes as entanglement resources, which are distributed using continuous-variable quantum repeaters. We find the optimal measurement on the teleported states, which uses beam splitters and photon-number-resolved detection. Compared to prior proposals relying on discrete states, our scheme has the advantages of using linear optics to implement it without wasting stellar photons, and making use of multiphoton events, which are regarded as noise in previous discrete schemes. We also outline the parameter regimes in which our scheme outperforms the direct detection method, schemes utilizing distributed discrete-variable entangled states, and local heterodyne techniques. 

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4. All-photonic Gottesman-Kitaev-Preskill–qubit repeater using analog-information-assisted multiplexed entanglement ranking

   https://doi.org/10.1103/PhysRevResearch.5.043056  

   Rozpędek, Filip; Seshadreesan, Kaushik P; Polakos, Paul; Jiang, Liang; Guha, Saikat (October 2023, Physical Review Research)

   Long-distance quantum communication will require the use of quantum repeaters to overcome the exponential attenuation of signal with distance. One class of such repeaters utilizes quantum error correction to overcome losses in the communication channel. Here we propose a strategy of using the bosonic Gottesman-Kitaev-Preskill (GKP) code in a two-way repeater architecture with multiplexing. The crucial feature of the GKP code that we make use of is the fact that GKP qubits easily admit deterministic two-qubit gates, hence allowing for multiplexing without the need for generating large cluster states as required in previous all-photonic architectures based on discrete-variable codes. Moreover, alleviating the need for such clique clusters entails that we are no longer limited to extraction of at most one end-to-end entangled pair from a single protocol run. In fact, thanks to the availability of the analog information generated during the measurements of the GKP qubits, we can design better entanglement swapping procedures in which we connect links based on their estimated quality. This enables us to use all the multiplexed links so that large number of links from a single protocol run can contribute to the generation of the end-to-end entanglement. We find that our architecture allows for high-rate end-to-end entanglement generation and is resilient to imperfections arising from finite squeezing in the GKP state preparation and homodyne detection inefficiency. In particular we show that long-distance quantum communication over more than 1000 km is possible even with less than 13 dB of GKP squeezing. We also quantify the number of GKP qubits needed for the implementation of our scheme and find that for good hardware parameters our scheme requires around 10^3 - 10^4 GKP qubits per repeater per protocol run. 

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5. Bridging the Capacity Gap Between Interactive and One-Way Communication

   https://doi.org/10.1137/1.9781611974782.138  

   Haeupler, Bernhard; Velingker, Ameya (October 2017, ACM-SIAM Symposium on Discrete Algorithms)

   We study the communication rate of coding schemes for interactive communication that transform any two-party interactive protocol into a protocol that is robust to noise. Recently, Haeupler [11] showed that if an ∊ > 0 fraction of transmissions are corrupted, adversarially or randomly, then it is possible to achieve a communication rate of Furthermore, Haeupler conjectured that this rate is optimal for general input protocols. This stands in contrast to the classical setting of one-way communication in which error-correcting codes are known to achieve an optimal communication rate of 1 In this work, we show that the quadratically smaller rate loss of the one-way setting can also be achieved in interactive coding schemes for a very natural class of input protocols. We introduce the notion of average message length, or the average number of bits a party sends before receiving a reply, as a natural parameter for measuring the level of interactivity in a protocol. Moreover, we show that any protocol with average message length ℓ = Ω(poly(1/∊)) can be simulated by a protocol with optimal communication rate 1 - Θ(Η(∊)) over an oblivious adversarial channel with error fraction e. Furthermore, under the additional assumption of access to public shared randomness, the optimal communication rate is achieved ratelessly, i.e., the communication rate adapts automatically to the actual error rate e without having to specify it in advance. This shows that the capacity gap between one-way and interactive communication can be bridged even for very small (constant in e) average message lengths, which are likely to be found in many applications. 

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