Quantum communication networks based on fiber optics are restricted in length since efficient quantum repeaters are not yet available. A free-space channel between a satellite in orbit and Earth can circumvent this problem. We have constructed a system to demonstrate the feasibility of quantum communication between space and earth using photons hyperentangled in their polarization and time-bin degrees of freedom. With this system, we have implemented superdense teleportation (SDT) with a fidelity of 0.94±0.02. To increase the efficiency of SDT, we have developed an active, polarization-independent switch compatible with SDT. We characterized the performance of its switching efficiency. Finally, we have constructed a novel two-level interferometer for time-bin qubit creation and analysis in orbit, and bounded its stability.
Quantum communication networks based on fiber optics are restricted in length since efficient quantum repeaters are not yet available. A free-space channel between a satellite in orbit and Earth can circumvent this problem. We have constructed a system to demonstrate the feasibility of quantum communication between space and earth using photons hyperentangled in their polarization and time-bin degrees of freedom. With this system, we have implemented superdense teleportation (SDT) with a fidelity of 0.94±0.02. To increase the efficiency of SDT, we have developed an active, polarization-independent switch compatible with SDT. We characterized the performance of its switching efficiency. Finally, we have constructed a novel two-level interferometer for time-bin qubit creation and analysis in orbit, and bounded its stability.
To build a global quantum-communication network, low-transmission, fiber-based communication channels can be supplemented by using a free-space channel between a satellite and a ground station on Earth. We construct a system that generates hyperentangled photonic ``ququarts'' and measures them to execute multiple quantum-communication protocols of interest. We successfully execute and characterize superdense teleportation, a modified remote-state preparation protocol that transfers more quantum information than standard teleportation, for the same classical information cost, and moreover, is in principle deterministic. Our measurements show an average fidelity of $0.94\ifmmode\pm\else\textpm\fi{}0.02$, with a phase resolution of approximately ${7}^{\ensuremath{\circ}}$, allowing reliable transmission of >105 distinguishable quantum states. Additionally, we demonstrate the ability to compensate for the Doppler shift, which would otherwise prevent sending time-bin encoded states from a rapidly moving satellite, thus allowing the low-error execution of phase-sensitive protocols during an orbital pass. Finally, we show that the estimated number of received coincidence counts in a realistic implementation is sufficient to enable faithful reconstruction of the received state in a single pass.
Superdense Teleportation (SDT) is a suitable protocol to choose for an advanced demonstration of quantum communication in space. We have taken further steps towards the realization of SDT in such an endeavor. Our system uses polarization and time-bin hyperentanglement via non-degenerate spontaneous parametric downconversion to implement SDT of 4-dimensional equimodular states. Previously, we have shown high fidelity (>90%) SDT implementation and the feasibility to perform SDT on an orbiting platform by correcting the Doppler shift. Here we discuss new analysis of the received state reconstruction performance in the presence of high channel loss and multiple pair events. Additionally, initial characterization of a waveguide-based entanglement source intended for space will be presented.
The transfer of quantum information over long distances has long been a goal of quantum information science and is required for many important quantum communication and computing protocols. When these channels are lossy and noisy, it is often impossible to directly transmit quantum states between two distant parties. We use a new technique called superdense teleportation to communicate quantum information deterministically with greatly reduced resources, simplified measurements, and decreased classical communication cost. These advantages make this technique ideal for communicating quantum information for space applications. We are currently implementing an superdense teleportation lab demonstration, using photons hyperentangled in polarization and temporal mode to communicate a special set of two-qubit, single-photon states between two remote parties. A slight modification of the system readily allows it to be used to implement quantum cryptography as well. We investigate the possibility of implementation from an Earth's orbit to ground. We will discuss our current experimental progress and the design challenges facing a practical demonstration of satellite-to-Earth SDT.
Establishing a quantum communication network would provide advantages in areas such as security and information processing. Such a network would require the implementation of quantum teleportation between remote parties. However, for photonic "qudits" of dimension greater than two, this teleportation always fails due to the inability to carry out the required quantum Bell-state measurement. A quantum communication protocol called Superdense Teleportation (SDT) can allow the reconstruction of a state without the usual 2-photon Bell-state measurements, enabling the protocol to succeed deterministically even for high dimensional qudits. This technique restricts the class of states transferred to equimodular states, a type of superposition state where each term can differ from the others in phase but not in amplitude; this restricted space of transmitted states allows the transfer to occur deterministically. We report on our implementation of SDT using photon pairs that are entangled in both polarization and temporal mode. After encoding the phases of the desired equimodular state on the signal photon, we perform a complete tomography on the idler photon to verify that we properly prepared the chosen state. Beyond our tabletop demonstration, we are working towards an implementation between a space platform in low earth orbit and a ground telescope, to demonstrate the feasibility of space-based quantum communication. We will discuss the various challenges presented by moving the experiment out of the laboratory, and our proposed solutions to make Superdense Teleportation realizable in the space setting.
Fiber-based quantum communication networks are currently limited without quantum repeaters. Satellite-based quantum links have been proposed to extend the network domain. We develop a quantum communication system, suitable for realistic satellite-to-ground communication. With this system, we execute an entanglement-based quantum key distribution (QKD) protocol developed by Bennett, Brassard, and Mermin (BBM92), achieving quantum bit-error rates (QBERs) below 2% in all bases. More importantly, we demonstrate low-QBER execution of a higher-dimensional hyperentanglement-based QKD protocol, using photons simultaneously entangled in polarization and time bin, leading to significantly higher secure key rates, at the cost of increased technical complexity and system size. We show that our protocol is suitable for a space-to-ground link, after incorporating Doppler-shift compensation, and verify its security using a rigorous finite-key analysis. Additionally, we discuss system-engineering considerations relevant to those and other quantum communication protocols and their dependence on what photonic degrees of freedom are utilized.
This work deals with creation, manipulation and detection of quantum photon states, in one and two degrees of freedom, encoded in polarization and time-bin basis. A particular quantum state, an entangled state, carries a wide range of implementations, that are impossible via classical tasks, such as teleportation, dense coding, and quantum communication protocols. One of these tasks, quantum cryptography, allows intrinsically secure transmission of information. Nowadays, quantum key distribution is implemented in intercity quantum networks, by using telecommunication fibers to connect nodes within the network. In future scenarios, photons could travel through greater distances, but, due to losses, fiber links need for quantum repeater, a very demanding engineering solution. An alternative way, is the use of free-space satellite quantum networks. Here we focus on polarization and time bin degrees of freedom (DOFs) of the photons as a resource for quantum information. In particular we study the possibility to share an hyper-entangled state in polarization and time-bin DOFs between two spatially separated users. In addition we study a new tomographic method, based on compressed sensing, to recover the density matrix of a quantum state when prior information are available. Typical implementation of time-bin photon source, based on Franson’s scheme, suffers on intrinsic loophole. To overcome that we experimentally demonstrated that with a time-bin source it is possible to obtain a very high visibility in order to violate a chained Bell inequality. Interference at single photon level through satellite-ground channels is presented here, showing that, temporal encoding is preserved along turbulent channels. With this experiment we show that temporal encoding can be use for a future implementation of satellite quantum communication. Finally, to complete this work, we demonstrate a new method to certified the randomness of a source, useful in many task, such as quantum cryptography by using a polarization entangled photons source.