In this paper, we focus on quantum communication systems that facilitate either secure data transfer or quantum key distribution via free-space links. Unlike classical channels where the effects of turbulent media on the optical wave front is well known and can be predicted with existing theoretical models, the mechanism described in the latter cannot be directly applied to quantum states. In our approach that relies on emitting correlated photon pairs with polarization entanglement, another realm of problems is encountered, which is not related to wave front distortions, but rather to integrity of the quantum states. Proper response of the detection system to non-classical features of light requires that photon pairs with proper polarization arrive to the receiver and their correlation characteristics are still preserved. Therefore, it is necessary to research a wide array of operating conditions corresponding to different levels of turbulence and finding proper mechanisms to replicate those on our laboratory testbed. In this paper, we present a system that integrates an atmospheric chamber developed by the AFRL, a link emulating quantum communication and analysis instrumentation. A system is developed that allows scaling the experiments over different ranges and quantitative analysis of entanglement characteristics of the received signals. Integrity of the quantum states is evaluated under practical operating conditions.
Quantum entanglement is an essential element for building the backbone of quantum information systems. Our particular interest lies in long-range distribution of entangled photons to facilitate secure data transfer in free space. To achieve this, we rely on photon pairs generated in such a way that their polarization characteristics represent the corresponding qubit states and have a high degree of correlation in measurements. The main focus of this paper is integrity of the quantum states in free-space channels. When transmitted in atmosphere, classical signals suffer from wave front distortions caused by the spatial and temporal fields of the refractive index. However, this mechanism does not have the same bearing on qubit values and their correlation. We study the effects of turbulence on quantum states by utilizing a laboratory testbed that includes an atmospheric chamber developed by the AFRL. It uses a system of controlled components capable of creating various turbulence conditions. When polarized signals are passed through the atmospheric chamber, we analyze the corresponding quantum states and evaluate the degree of entanglement using our mathematical models and existing metrics.
An outstanding challenge in quantum networking is interfacing both classical and quantum technologies. A future quantum network will require one to effectively interface disparate qubit for entanglement distribution applications. In addition, the quantum network will also need to be seamlessly integrated with a classical network to realize the quantum protocols. This talk will highlight recent results toward interfacing integrated photonic qubits, trapped ions, and superconducting qubits and will present progress toward constructing a classical network infrastructure and initial results on operating the classical and quantum network in unison.
Quantum computing (QC) is theorized to solve certain important problems much faster than classical computers. The current state of QC, the noisy intermediate-scale quantum (NISQ) era, is limited in the scope of problems it can solve, largely due to the quantity of reliable qubits available to universal quantum operations. And while all available quantum computing systems have their advantages, ion-based systems have been shown to be a reliable option with low infidelity and a capability for universal gating procedure. These advantages are dependent on achieving low crosstalk when addressing ions, a vital challenge for this QC system, particularly when using only bulk optic systems. Here we show a microfabricated planar waveguide which can selectively interact in free space with 8 trapped Ba+ ions. This performance meets or exceeds that of similar waveguides couple to trapped ion systems and shows a reliable method to selectively interact with ions bound by a Paul Trap using imaged waveguide outputs.
Free-Space Optical (FSO) communication holds the potential for data communications at high bandwidths security while minimizing size, weight, and power (SWAP). However, the effects of atmospheric turbulence on an optical beam during propagation limits and degrades communication performance and bit-error-rate. Although degradation of beam quality occurs due to many factors, typically unwanted aberrations due to fluctuations in the refractive index n along beam path causing scattering, absorption, and beam wander is the main cause. Randomly distributed cells called eddies are formed in the propagating medium giving rise to turbulence as well. In this paper, we report experimental results from a 3-meter FSO data link. An intensity modulated 10 Gbps beam in the next phase will be analyzed and correlated to real time weather. We study scintillations and deviation of the beam from its original path (beam wander and spread). A phosphor-coated silicon CCD is used to record and study the beam’s intensity profile.
The primary focus of this paper is high-performance quantum communication systems that facilitate secure data transfer via free-space links. We consider an approach that uses correlated photon pairs generated in such a way that their polarizations are entangled and can be used to support quantum encryption protocols. However, when deployed in free space, these links can be affected by channel distortion, primarily via the spatial and temporal fields of the refractive index along the propagation path. In classical links, these fields alter the optical wave front characteristics; however, this mechanism does not directly apply to the quantum states utilized in single-photon or entangled photon protocols. Transmitting signals with quantum-based encryption creates a realm of problems, not related to wave front distortions, but rather to integrity of the quantum states after the signals propagate over free-space channels. We study these phenomena by implementing a laboratory testbed capable of creating a turbulent environment using atmospheric chambers developed by the AFRL. It is then used for experimental investigation of quantum entanglement after photon pairs are propagated both collinearly and via separate paths.
Free-space optical communication (FSOC) holds unmatched potential for high bandwidth and secure communications while minimizing size, weight, and power (SWAP). However, the effects of atmospheric scintillations on high bandwidth signals limits data link performance by degrading OSNR (Optical signal-to-noise ratio) and Q-factor. A critical component due to which a communication signal quality deteriorates is timing jitter. Jitter may be due to timing of the data signal or it may be due to the amplitude variations in the data bit stream as it propagates through free-space. As the data bandwidth increases, these effects become more significant. A small-time deviation in a lower data rate signal which would be tolerable or be above a receiver sensitivity, turns into an intolerable signal at higher data rates as jitter increases. The total jitter (TJ) can be further broken down to deterministic jitter (DJ) and random jitter (RJ). These may help understand signal behavior and the root cause of degradation in a FSOC or any data communication link. Thus, for a system to achieve desired BER (bit-error-rate and bit-error-ratio), an in-depth analysis of jitter by investigating each of the subclass of both timing jitters, DJ and RJ, would be extremely helpful and enhance the robustness of the link. In this paper, we report in-depth jitter analysis from a FSOC data link at 10 Gbps propagating at 1550 nm.
The ability to distribute entanglement across a quantum network may lead to new capabilities like teleporting information over a difficult-to-access quantum channel or higher resolution quantum sensors. However, there are many outstanding challenges to realizing such a quantum network. One of these challenges is how to interface disparate quantum technologies effectively and efficiently. Ultimately a quantum network will be used to connect different types of devices, much like the current internet does today, and this requires one to seamlessly connect qubit technologies operating in vastly different environments. This talk will present results on interfacing trapped ion qubits to quantum integrated photonic circuits and discuss challenges related to interfacing trapped ion qubits with superconducting qubits.
Quantum entanglement is critical to build the backbone of all quantum technologies. Quantum networks, quantum computations, and quantum communication networking is based on long-range distribution of entangled photons and teleportation of photon qubit states. In order to understand quantum entanglement, characterization of atmospheric turbulence and its effects on propagating quantum states in free-space is essential. One method of photon entanglement is using a photon’s polarization. In this paper, we report results using polarization entangled signal and idler photons. The results may be applicable to support various quantum computing, encryption, and other qubit based high-performance communication protocols. Classically, the degradation of beam quality occurs due to many factors but primarily due to the distortion of spatial and temporal fields of refractive index. However, behavior of single photons through similar turbulent media creates a different set of challenges pointing to integrity of quantum states during propagation. We study this behavior by analyzing quantum states and the degree of entanglement in real-time and correlating it to known atmospheric models, (refractive index structure parameter), and relevant propagation path parameters. This experimental study was performed initially in a controlled laboratory environment, and then devised to be implemented outdoors over a 100-meter free space communication link.
We demonstrate the use of external field protocols to control optical properties of quantum spins for optimized photon-mediated operations in quantum information processing. Specifically, we study two-photon interference operations between spectrally different quantum emitters with realistic control protocols. We show that, well beyond their idealized versions, appropriate external field protocols can suppress spectral diffusion, mitigate inhomogeneous broadening and restore photon indistinguishability between spectrally different quantum emitters. These protocols can play an important role in enabling more efficient light-matter interfaces that are essential for scalable quantum information processing platforms.
KEYWORDS: Free space optics, Data communications, Signal attenuation, Scintillation, Turbulence, Eye, Free space optical communications, Atmospheric turbulence, Atmospheric propagation, Receivers
Free-space optical communication (FSOC) holds an unmatched potential for data communications with high bandwidth and security while minimizing size, weight, and power (SWAP). However, the effects of atmospheric turbulence on an optical wave during propagation limits and degrades communication performance. Although this degradation of beam quality occurs due to many factors, but unwanted aberrations due to scattering and absorption of the propagating electromagnetic wave is typically the primary cause. In this paper, we report experimental results from a free space optical FSO communication data link. Bandwidth up to 10 Gbps at 1550 nm is correlated to 𝑐𝑛2 (refractive index structure parameter), transmission wavelength, transmit and receive parameters. For further random and data dependent analysis, the communication link's transmission and receive data eye with amplitude and time jitter decomposition is performed using multiple NRZ PRBS patterns. Additionally, with the aim of reducing SWAP and cost, the experiment is built and designed mostly using off-the-shelf long-range single mode, small factor pluggable devices.
Atomic ions can be isolated from their environment through laser-cooling and trapping, making them useful for quantum information processing, measurement, and sensing. A variety of atomic ion species have been used as qubits. Hyperfine qubits with nuclear spin I = 1/2 have demonstrated the long qubit coherence times with simple, robust laser manipulation. Other qubits (I ≠ 1/2) have easily-prepared, long-lived metastable electronic excited states, and simple discrimination between these states allows high fidelity readout. However, none of the naturally- occurring, atomic ions with nuclear spin I = 1/2 have these excited states that are simultaneously long-lived and easy to prepare. We demonstrate loading, cooling, and qubit manipulation of an artificial, I = 1/2 species of barium with visible wavelength lasers: 133Ba+. We achieved a single shot qubit state preparation and readout fidelity of F = 0.9997, the lowest error rate ever achieved by any qubit on any platform.
Quantum information processing relies on the fundamental property of quantum interference, where the quality of the interference directly correlates to the indistinguishability of the interacting particles. The creation of these indistinguishable particles, photons in this case, has conventionally been accomplished with nonlinear crystals and optical filters to remove spectral distinguishability, albeit sacrificing the number of photons. This research describes the use of an integrated aluminum nitride microring resonator circuit to selectively generate photon pairs at the narrow cavity transmissions, thereby producing spectrally indistinguishable photons in the ultraviolet regime to interact with trapped ion quantum memories. The spectral characteristics of these photons must be carefully controlled for two reasons: (i) interference quality depends on the spectral indistinguishability, and (ii) the wavelength must be strictly controlled to interact with atomic transitions. The specific ion of interest for these trapped ion quantum memories is Ytterbium which has a transition at 369.5 nm with 12.5 GHz offset levels. Ytterbium ions serve as very long lived and stable quantum memories with storage times on the order of 10’s of minutes, compared with photonic quantum memories which are limited to 10-6 to 10-3 seconds. The combination of the long lived atomic memory, integrated photonic circuitry, and the photonic quantum bits are necessary to produce the first quantum information processors. In this seminar, I will present results on ultraviolet wavelength operation, dispersion analysis, and propagation loss in aluminum nitride waveguides.
B. Tabakov, J. Bell, D. Bogorin, B. Bonenfant, P. Cook, L. Disney, T. Dolezal, J. O'Reilly, J. Phillips, K. Poole, L. Wessing, K.-A. Brickman-Soderberg
Quantum networking exploits features of quantum mechanics to provide ultrasecure networks that are both tamper-proof and tamper-evident. Such networks can be implemented as distant memory nodes connected via photon-based interfaces. Trapped ions are nearly ideal quantum network nodes due to the precise control possible over both their internal and external degrees of freedom as well as for their superior performance as long-term quantum memories. Photon-based qubits are the natural choice to transfer information within the network due to their ability to transmit quantum information over long distances and the capability to process information ”on-the-fly” between the memory nodes. We present the quantum research being done at the Air Force Research Laboratory (AFRL) with a focus on trapped ion qubits, the short- and long-term goals of the lab, and some of the unique resources we have access to at AFRL.
Quantum information processing relies on the fundamental property of quantum interference, where the quality of the interference directly correlates to the indistinguishability of the interacting particles. The creation of these indistinguishable particles, photons in this case, has conventionally been accomplished with nonlinear crystals and optical filters to remove spectral distinguishability, albeit sacrificing the number of photons. This research describes the use of an integrated aluminum nitride microring resonator circuit to selectively generate photon pairs at the narrow cavity transmissions, thereby producing spectrally indistinguishable photons. These spectrally indistinguishable photons can then be routed through optical waveguide circuitry, concatenated interferometers, to manipulate and entangle the photons into the desired quantum states. Photon sources and circuitry are only two of the three required pieces of the puzzle. The final piece which this research is aimed at interfacing with are trapped ion quantum memories, based on trapped Ytterbium ions. These ions serve as very long lived and stable quantum memories with storage times on the order of 10’s of minutes, compared with photonic quantum memories which are limited to 10-6 to 10-3 seconds. The caveat with trapped ions is the interaction wavelength of the photons is 369.5nm and therefore the goal of this research is to develop entangled photon sources and circuitry in that wavelength regime to interact directly with the trapped ions and bypass the need for frequency conversion.
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