Entanglement-based quantum digital signatures over a deployed campus network.

The quantum digital signature protocol offers a replacement for most aspects of public-key digital signatures ubiquitous in today's digital world. A major advantage of a quantum-digital-signatures protocol is that it can have information-theoretic security, whereas public-key cryptography cannot. Here we demonstrate and characterize hardware to implement entanglement-based quantum digital signatures over our campus network. Over 25 hours, we collect measurements on our campus network, where we measure sufficiently low quantum bit error rates (<5% in most cases) which in principle enable quantum digital signatures at over 50 km as shown through rigorous simulation accompanied by a noise model developed specifically for our implementation. These results show quantum digital signatures can be successfully employed over deployed fiber. Moreover, our reported method provides great flexibility in the number of users, but with reduced entanglement rate per user. Finally, while the current implementation of our entanglement-based approach has a low signature rate, feasible upgrades would significantly increase the signature rate.

Quantum Key Distribution for Critical Infrastructures: Towards Cyber-Physical Security for Hydropower and Dams.

Hydropower facilities are often remotely monitored or controlled from a centralized remote control room. Additionally, major component manufacturers monitor the performance of installed components, increasingly via public communication infrastructures. While these communications enable efficiencies and increased reliability, they also expand the cyber-attack surface. Communications may use the internet to remote control a facility's control systems, or it may involve sending control commands over a network from a control room to a machine. The content could be encrypted and decrypted using a public key to protect the communicated information. These cryptographic encoding and decoding schemes become vulnerable as more advances are made in computer technologies, such as quantum computing. In contrast, quantum key distribution (QKD) and other quantum cryptographic protocols are not based upon a computational problem, and offer an alternative to symmetric cryptography in some scenarios. Although the underlying mechanism of quantum cryptogrpahic protocols such as QKD ensure that any attempt by an adversary to observe the quantum part of the protocol will result in a detectable signature as an increased error rate, potentially even preventing key generation, it serves as a warning for further investigation. In QKD, when the error rate is low enough and enough photons have been detected, a shared private key can be generated known only to the sender and receiver. We describe how this novel technology and its several modalities could benefit the critical infrastructures of dams or hydropower facilities. The presented discussions may be viewed as a precursor to a quantum cybersecurity roadmap for the identification of relevant threats and mitigation.

Generation and characterization of ultrabroadband polarization-frequency hyperentangled photons.

We generate ultrabroadband photon pairs entangled in both polarization and frequency bins through an all-waveguided Sagnac source covering the entire optical C- and L-bands (1530-1625 nm). We perform comprehensive characterization of high-fidelity states in multiple dense wavelength-division multiplexed channels, achieving full tomography of effective four-qubit systems. Additionally, leveraging the inherent high dimensionality of frequency encoding and our electro-optic measurement approach, we demonstrate the scalability of our system to higher dimensions, reconstructing states in a 36-dimensional Hilbert space consisting of two polarization qubits and two frequency-bin qutrits. Our findings hold potential significance for quantum networking, particularly dense coding and entanglement distillation in wavelength-multiplexed quantum networks.

Two-mode squeezing over deployed fiber coexisting with conventional communications.

Squeezed light is a crucial resource for continuous-variable (CV) quantum information science. Distributed multi-mode squeezing is critical for enabling CV quantum networks and distributed quantum sensing. To date, multi-mode squeezing measured by homodyne detection has been limited to single-room experiments without coexisting classical signals, i.e., on "dark" fiber. Here, after distribution through separate fiber spools (5 km), -0.9 ± 0.1-dB coexistent two-mode squeezing is measured. Moreover, after distribution through separate deployed campus fibers (about 250 m and 1.2 km), -0.5 ± 0.1-dB coexistent two-mode squeezing is measured. Prior to distribution, the squeezed modes are each frequency multiplexed with several classical signals-including the local oscillator and conventional network signals-demonstrating that the squeezed modes do not need dedicated dark fiber. After distribution, joint two-mode squeezing is measured and recorded for post-processing using triggered homodyne detection in separate locations. This demonstration enables future applications in quantum networks and quantum sensing that rely on distributed multi-mode squeezing.

Space-based quantum networking in the presence of a nuclear disturbed environment.

Space-based quantum networks provide a means for near-term long-distance transmission of quantum information. This article analyzed the performance of a downlink quantum network between a low-Earth-orbit satellite and an observatory operating in less-than-ideal atmospheric conditions. The effects from fog, haze, and a nuclear disturbed environment on the long-range distribution of quantum states were investigated. A density matrix that estimates the quantum state by capturing the effects from increased signal loss and elevated background noise to estimate the state fidelity of the transmitted quantum state was developed. It was found that the nuclear disturbed environment and other atmospheric effects have a degrading effect on the quantum state. These environments impede the ability to perform quantum communications for the duration of the effects. In the case of the nuclear disturbed environment, the nuclear effects subside quickly, and network performance should return to normal by the next satellite pass.

Effects of a nuclear-disturbed environment on electromagnetic wave propagation through the atmosphere.

This paper investigates the effects of a nuclear-disturbed environment on the transmission of electromagnetic (EM) waves through the atmosphere. An atmospheric nuclear detonation can produce heightened free electron densities in the surrounding atmosphere that can disrupt EM waves that propagate through the disturbed region. Radiation transport models simulated the ionization and free electron densities created in the atmosphere from a 1 MT detonation at heights of burst of 5 km, 25 km, and 75 km. Recombination rates for the free electrons in the atmosphere were applied, from previous work in the literature, to determine the nuclear-induced electron densities as a function of time and space after the detonation. A ray-tracing algorithm was applied to determine the refraction and reflection of waves propagating in the different nuclear-disturbed environments. The simulation results show that the free electron plasma created from an atmospheric nuclear detonation depend on the height of burst of the weapon, the weapon yield, and the time after detonation. Detonations at higher altitudes produce higher free electron densities for greater durations and over larger ranges. The larger the free electron densities, the greater the impact on EM wavelengths in regards to refraction, reflection, and absorption in the atmosphere. An analysis of modern infrastructure and the effects of nuclear-disturbed atmospheres on different signal wavelengths and systems is discussed.

Bayesian homodyne and heterodyne tomography: erratum.

We correct typographical errors in Eq. (15) in [Opt. Express30, 15184 (2022)10.1364/OE.456597] [1]. These errors were not present in the actual formulas used to calculate the results of the paper, so all results remain unaffected.

Broadband polarization-entangled source for C+L-band flex-grid quantum networks.

The rising demand for transmission capacity in optical networks has motivated steady interest in expansion beyond the standard C-band (1530-1565 nm) into the adjacent L-band (1565-1625 nm) for an approximate doubling of capacity in a single stroke. However, in the context of quantum networking, the L-band has yet to be fully leveraged with the suite of advanced tools for characterization and management available from classical lightwave communications. In this work, we demonstrate an ultrabroadband two-photon source integrating both C- and L-band wavelength-selective switches for complete control of spectral routing and allocation across 7.5 THz in a single setup. Polarization state tomography of all 150 pairs of 25-GHz-wide channels reveals an average fidelity of 0.98 and total distillable entanglement greater than 181 kebits/s. This source is explicitly designed for flex-grid optical networks and can facilitate optimal utilization of entanglement resources across the full C+L-band.

Optimal resource allocation for flexible-grid entanglement distribution networks.

We use a genetic algorithm (GA) as a design aid for determining the optimal provisioning of entangled photon spectrum in flex-grid quantum networks with arbitrary numbers of channels and users. After introducing a general model for entanglement distribution based on frequency-polarization hyperentangled biphotons, we derive upper bounds on fidelity and entangled bit rate for networks comprising one-to-one user connections. Simple conditions based on user detector quality and link efficiencies are found that determine whether entanglement is possible. We successfully apply a GA to find optimal resource allocations in four different representative network scenarios and validate features of our model experimentally in a quantum local area network in deployed fiber. Our results show promise for the rapid design of large-scale entanglement distribution networks.

Heterodyne spectrometer sensitivity limit for quantum networking.

Optical heterodyne detection-based spectrometers are attractive due to their relatively simple construction and ultrahigh resolution. Here we demonstrate a proof-of-principle single-mode optical-fiber-based heterodyne spectrometer that has picometer resolution and quantum-limited sensitivity around 1550 nm. Moreover, we report a generalized quantum limit of detecting broadband multispectral-temporal-mode light using heterodyne detection, which provides a sensitivity limit on a heterodyne detection-based optical spectrometer. We then compare this sensitivity limit to several spectrometer types and dim light sources of interest such as spontaneous parametric downconversion, Raman scattering, and spontaneous four-wave mixing. We calculate that the heterodyne spectrometer is significantly less sensitive than a single-photon detector and is unable to detect these dim light sources, except for the brightest and narrowest-bandwidth examples.

Authentication of smart grid communications using quantum key distribution.

Smart grid solutions enable utilities and customers to better monitor and control energy use via information and communications technology. Information technology is intended to improve the future electric grid's reliability, efficiency, and sustainability by implementing advanced monitoring and control systems. However, leveraging modern communications systems also makes the grid vulnerable to cyberattacks. Here we report the first use of quantum key distribution (QKD) keys in the authentication of smart grid communications. In particular, we make such demonstration on a deployed electric utility fiber network. The developed method was prototyped in a software package to manage and utilize cryptographic keys to authenticate machine-to-machine communications used for supervisory control and data acquisition (SCADA). This demonstration showcases the feasibility of using QKD to improve the security of critical infrastructure, including future distributed energy resources (DERs), such as energy storage.

Bayesian homodyne and heterodyne tomography.

Continuous-variable (CV) photonic states are of increasing interest in quantum information science, bolstered by features such as deterministic resource state generation and error correction via bosonic codes. Data-efficient characterization methods will prove critical in the fine-tuning and maturation of such CV quantum technology. Although Bayesian inference offers appealing properties-including uncertainty quantification and optimality in mean-squared error-Bayesian methods have yet to be demonstrated for the tomography of arbitrary CV states. Here we introduce a complete Bayesian quantum state tomography workflow capable of inferring generic CV states measured by homodyne or heterodyne detection, with no assumption of Gaussianity. As examples, we demonstrate our approach on experimental coherent, thermal, and cat state data, obtaining excellent agreement between our Bayesian estimates and theoretical predictions. Our approach lays the groundwork for Bayesian estimation of highly complex CV quantum states in emerging quantum photonic platforms, such as quantum communications networks and sensors.

Putting midodrine on the MAP: An approach to liberation from intravenous vasopressors in vasodilatory shock.

PURPOSE: Prolonged duration of intravenous (IV) vasopressor dependence in critically ill adult patients with vasodilatory shock results in increased length of stay in both the intensive care unit (ICU) and hospital, translating to higher risk of infection, delirium, immobility, and cost. Acceleration of vasopressor liberation can aid in reducing these risks. Midodrine is an oral α 1-adrenergic receptor agonist that offers a potential means of liberating patients from IV vasopressor therapy. This clinical review summarizes primary literature and proposes a clinical application for midodrine in the recovery phase of vasodilatory shock. SUMMARY: Five studies with a total of over 1,000 patients conducted between 2011 and 2021 were identified. In observational studies, midodrine administration was demonstrated to lead to faster time to liberation from IV vasopressor therapy and shorter ICU length of stay in patients recovering from vasodilatory shock. These findings were not replicated in a prospective, multicenter, randomized controlled trial. In this review, literature evaluating midodrine use for IV vasopressor liberation is summarized and study limitations are discussed. CONCLUSION: On the basis of this review of current literature, recommendations are provided on selecting appropriate candidates for adjunctive midodrine in the recovery phase of vasodilatory shock and considerations are discussed for safely and effectively initiating, titrating, and discontinuing therapy.

The Concept of a Quantum Edge Simulator: Edge Computing and Sensing in the Quantum Era.

Sensors, enabling observations across vast spatial, spectral, and temporal scales, are major data generators for information technology (IT). Processing, storing, and communicating this ever-growing amount of data pose challenges for the current IT infrastructure. Edge computing-an emerging paradigm to overcome the shortcomings of cloud-based computing-could address these challenges. Furthermore, emerging technologies such as quantum computing, quantum sensing, and quantum communications have the potential to fill the performance gaps left by their classical counterparts. Here, we present the concept of an edge quantum computing (EQC) simulator-a platform for designing the next generation of edge computing applications. An EQC simulator is envisioned to integrate elements from both quantum technologies and edge computing to allow studies of quantum edge applications. The presented concept is motivated by the increasing demand for more sensitive and precise sensors that can operate faster at lower power consumption, generating both larger and denser datasets. These demands may be fulfilled with edge quantum sensor networks. Envisioning the EQC era, we present our view on how such a scenario may be amenable to quantification and design. Given the cost and complexity of quantum systems, constructing physical prototypes to explore design and optimization spaces is not sustainable, necessitating EQC infrastructure and component simulators to aid in co-design. We discuss what such a simulator may entail and possible use cases that invoke quantum computing at the edge integrated with new sensor infrastructures.

Effects of a nuclear disturbed environment on a quantum free space optical link.

This manuscript investigates the potential effect of a nuclear-disturbed atmospheric environment on the signal attenuation of a ground/satellite transmitter/receiver system for both classical optical and quantum communications applications. Attenuation of a signal transmitted through the rising nuclear cloud and the subsequently transported debris is modeled climatologically for surface-level detonations of 10 kt, 100 kt, and 1 Mt. Attenuation statistics were collected as a function of time after detonation. These loss terms were compared to normal loss sources such as clouds, smoke from fires, and clear sky operation. Finally, the loss was related to the degradation of transmitted entanglement derived from Bayesian mean estimation.

Electro-Optic Frequency Beam Splitters and Tritters for High-Fidelity Photonic Quantum Information Processing.

We report the experimental realization of high-fidelity photonic quantum gates for frequency-encoded qubits and qutrits based on electro-optic modulation and Fourier-transform pulse shaping. Our frequency version of the Hadamard gate offers near-unity fidelity (0.99998±0.00003), requires only a single microwave drive tone for near-ideal performance, functions across the entire C band (1530-1570 nm), and can operate concurrently on multiple qubits spaced as tightly as four frequency modes apart, with no observable degradation in the fidelity. For qutrits, we implement a 3×3 extension of the Hadamard gate: the balanced tritter. This tritter-the first ever demonstrated for frequency modes-attains fidelity 0.9989±0.0004. These gates represent important building blocks toward scalable, high-fidelity quantum information processing based on frequency encoding.

Naturally stable Sagnac-Michelson nonlinear interferometer.

Interferometers measure a wide variety of dynamic processes by converting a phase change into an intensity change. Nonlinear interferometers, making use of nonlinear media in lieu of beamsplitters, promise substantial improvement in the quest to reach the ultimate sensitivity limits. Here we demonstrate a new nonlinear interferometer utilizing a single parametric amplifier for mode mixing-conceptually, a nonlinear version of the conventional Michelson interferometer with its arms collapsed together. We observe up to 99.9% interference visibility and find evidence for noise reduction based on phase-sensitive gain. Our configuration utilizes fewer components than previous demonstrations and requires no active stabilization, offering new capabilities for practical nonlinear interferometric-based sensors.

On the general constraints in single qubit quantum process tomography.

We briefly review single-qubit quantum process tomography for trace-preserving and nontrace-preserving processes, and derive explicit forms of the general constraints for fitting experimental data. These forms provide additional insight into the structure of the process matrix. We illustrate this with several examples, including a discussion of qubit leakage error models and the intuition which can be gained from their process matrices.

Loss resilience for two-qubit state transmission using distributed phase sensitive amplification.

We transmit phase-encoded non-orthogonal quantum states through a 5-km long fibre-based distributed optical phase-sensitive amplifier (OPSA) using telecom-wavelength photonic qubit pairs. The gain is set to equal the transmission loss to probabilistically preserve input states during transmission. While neither state is optimally aligned to the OPSA, each input state is equally amplified with no measurable degradation in state quality. These results promise a new approach to reduce the effects of loss by encoding quantum information in a two-qubit Hilbert space which is designed to benefit from transmission through an OPSA.

Alteplase for the Treatment of Pulmonary Embolism: A Review.

Pulmonary embolism can present with a wide range of symptoms, from asymptomatic to cardiac arrest, making diagnosis challenging. Alteplase is a fibrinolytic that is indicated for the treatment of pulmonary embolism in intermediate- and high-risk patients. Controversy exists as to the patient population that will benefit most from fibrinolytic therapy, as well as the proper dose and administration technique. The patient's risk of bleeding should be weighed against the potential benefits of treatment in light of the clinical presentation because of the high mortality rate associated with pulmonary embolism. Nurses at the bedside must monitor for signs of bleeding when alteplase is administered. Fibrinolytic therapy will frequently be started in the emergency department, and the nurse must ensure that alteplase is administered in a safe and effective manner. This review discusses the clinical evidence for alteplase in pulmonary embolism and its specific role in treatment.