Quantum Information Systems Research Articles

Quantum computing in controlling railroads

The paper discusses the main possibilities of using quantum computing and technologies in railway management, highlighting the most promising options and proposals for their application. One of the main objectives of the RZD "Russian Railways" is the research and implementation of quantum telecommunications as the basis for building promising network services. By focusing on improving solutions in the field of automation of railway transport process management, and taking into account the over-growing and changing needs of customers, RZD also wants to trans-form to digitalization and use quantum computing to create flexible management models, optimization of the structure and decision-making processes and the use of quantum computers both in information systems and in technical control systems. The study first identifies areas where the development of information technologies in railway transport is a must. Then the strategies and programs to digitalis these fields are discussed, how they are implemented is shown and finally a comparison is then made with other experiences from different agencies around the world. The Study concludes that the creation of quantum information systems with a contactless neuro-computer interface will solve several problems like the performance of duties by railway personnel, monitoring of significant objects of critical information and technical infrastructure, and public services. It is advisable to use quantum technologies and calculations in railway transport in the following main directions: the creation of a quantum telecommunication network; the introduction of quantum computing in the improvement of Blockchain technologies; use of quantum technologies to solve complex optimization problems.

A quantum-bit encoding converter

From telecommunications to computing architectures, the realm of classical information hinges on converter technology to enable the exchange of data between digital and analogue formats, a process now routinely performed across a variety of electronic devices. A similar exigency also exists in quantum information technology, where different frameworks are being developed for quantum computing, communication and sensing. Thus, efficient quantum interconnects are a major need to bring these parallel approaches together and scale up quantum information systems. So far, however, the conversion between different optical quantum-bit encodings has remained challenging due to the difficulty of preserving fragile quantum superpositions and the demanding requirements for postselection-free implementations. Here we demonstrate such a conversion of quantum information between the two main paradigms, namely discrete- and continuous-variable qubits. We certify the protocol on a complete set of single-photon qubits, successfully converting them to cat-state qubits with fidelities exceeding the classical limit. Our result demonstrates an essential tool for enabling interconnected quantum devices and architectures with enhanced versatility and scalability. A conversion of quantum information between single-photon and cat-state qubits is demonstrated by teleportation using optical hybrid entanglement. The classical limit of conversion is exceeded over the full Bloch sphere, with an average fidelity above 79%.

Ultra-low loss quantum photonic circuits integrated with single quantum emitters

The scaling of many photonic quantum information processing systems is ultimately limited by the flux of quantum light throughout an integrated photonic circuit. Source brightness and waveguide loss set basic limits on the on-chip photon flux. While substantial progress has been made, separately, towards ultra-low loss chip-scale photonic circuits and high brightness single-photon sources, integration of these technologies has remained elusive. Here, we report the integration of a quantum emitter single-photon source with a wafer-scale, ultra-low loss silicon nitride photonic circuit. We demonstrate triggered and pure single-photon emission into a Si3N4 photonic circuit with ≈ 1 dB/m propagation loss at a wavelength of ≈ 930 nm. We also observe resonance fluorescence in the strong drive regime, showing promise towards coherent control of quantum emitters. These results are a step forward towards scaled chip-integrated photonic quantum information systems in which storing, time-demultiplexing or buffering of deterministically generated single-photons is critical.

Spin-defect qubits in two-dimensional transition metal dichalcogenides operating at telecom wavelengths

Solid state quantum defects are promising candidates for scalable quantum information systems which can be seamlessly integrated with the conventional semiconductor electronic devices within the 3D monolithically integrated hybrid classical-quantum devices. Diamond nitrogen-vacancy (NV) center defects are the representative examples, but the controlled positioning of an NV center within bulk diamond is an outstanding challenge. Furthermore, quantum defect properties may not be easily tuned for bulk crystalline quantum defects. In comparison, 2D semiconductors, such as transition metal dichalcogenides (TMDs), are promising solid platform to host a quantum defect with tunable properties and a possibility of position control. Here, we computationally discover a promising defect family for spin qubit realization in 2D TMDs. The defects consist of transition metal atoms substituted at chalcogen sites with desirable spin-triplet ground state, zero-field splitting in the tens of GHz, and strong zero-phonon coupling to optical transitions in the highly desirable telecom band.

Tailoring Nonlinear Metamaterials for the Controlling of Spatial Quantum Entanglement.

The high designability of metamaterials has made them an attractive platform for devising novel optoelectronic devices. The demonstration of nonlinear metamaterials further indicates their potential in developing quantum applications. Here, we investigate designing nonlinear metamaterials consisting of the 3-fold (C3) rotationally symmetrical nanoantennas for generating and modulating entangled photons in the spatial degrees of freedom. Through tailoring the geometry and orientation of the nanoantennas, the parametric down conversion process inside the metamaterials can be locally engineered to generate entangled states with desired spatial properties. As the orbital angular momentum (OAM) states are valuable for enhancing the data capacity of quantum information systems, the photonic OAM entanglement is practically considered. With suitable nanostructure design, the generation of OAM entangled states is shown to be effectively realized in the discussed nonlinear metamaterial system. The nonlinear metamaterials present a perspective to provide a flexible platform for quantum photonic applications.

Qutrit-Inspired Fully Self-Supervised Shallow Quantum Learning Network for Brain Tumor Segmentation.

Classical self-supervised networks suffer from convergence problems and reduced segmentation accuracy due to forceful termination. Qubits or bilevel quantum bits often describe quantum neural network models. In this article, a novel self-supervised shallow learning network model exploiting the sophisticated three-level qutrit-inspired quantum information system, referred to as quantum fully self-supervised neural network (QFS-Net), is presented for automated segmentation of brain magnetic resonance (MR) images. The QFS-Net model comprises a trinity of a layered structure of qutrits interconnected through parametric Hadamard gates using an eight-connected second-order neighborhood-based topology. The nonlinear transformation of the qutrit states allows the underlying quantum neural network model to encode the quantum states, thereby enabling a faster self-organized counterpropagation of these states between the layers without supervision. The suggested QFS-Net model is tailored and extensively validated on the Cancer Imaging Archive (TCIA) dataset collected from the Nature repository. The experimental results are also compared with state-of-the-art supervised (U-Net and URes-Net architectures) and the self-supervised QIS-Net model and its classical counterpart. Results shed promising segmented outcomes in detecting tumors in terms of dice similarity and accuracy with minimum human intervention and computational resources. The proposed QFS-Net is also investigated on natural gray-scale images from the Berkeley segmentation dataset and yields promising outcomes in segmentation, thereby demonstrating the robustness of the QFS-Net model.

Optical-parametric oscillation in photonic-crystal ring resonators

By-design access to laser wavelength, especially with integrated photonics, is critical to advance quantum sensors, such as optical clocks and quantum-information systems, and open opportunities in optical communication. Semiconductor-laser gain provides exemplary efficiency and integration but merely in developed wavelength bands. Alternatively, nonlinear optics requires control of phase matching, but the principle of nonlinear conversion of a pump laser to a designed wavelength is extensible. We report on laser-wavelength access by versatile customization of optical-parametric oscillation (OPO) with a photonic-crystal ring resonator (PhCR). Leveraging the exquisite control of laser propagation provided by a photonic crystal in a traveling-wave ring resonator, we enable OPO generation across a wavelength range of 1234–2093 nm with a 1550-nm pump and 1016–1110 nm with a 1064-nm pump. Moreover, our platform offers pump-to-sideband conversion efficiency of > 10 % and negligible additive optical-frequency noise across the output range. From laser design to simulation of nonlinear dynamics, we use a Lugiato–Lefever framework that predicts the system characteristics, including bidirectional OPO generation in the PhCR and conversion efficiency in agreement with our observations. Our experiments introduce broadband lasers by design with PhCR OPOs, providing critical functionalities in integrated photonics.

Algebraic representation of Three Qubit Quantum Circuit Problems

The evolution of quantum states serves as good fundamental studies in understanding the quantum information systems which finally lead to the research on quantum computation. To carry out such a study, mathematical tools such as the Lie group and their associated Lie algebra is of great importance. In this study, the Lie algebra of su(8) is represented in a tensor product operation between three Pauli matrices. This can be realized by constructing the generalized Gell-Mann matrices and comparing them to the Pauli bases. It is shown that there is a one-to-one correlation of the Gell-Mann matrices with the Pauli basis which resembled the change of coordinates. Together with the commutator relations and the frequency analysis of the structure constant via the algebra, the Lie bracket operation will be highlighted providing insight into relating quantum circuit model with Lie Algebra. These are particularly useful when dealing with three-qubit quantum circuit problems which involve quantum gates that is derived from the SU(8) Lie group.

Very sensitive probes for quantitative and organoleptic detection of oxygen based on conformer-induced room-temperature phosphorescence enhancement of the derivative of triazatruxene and phenothiazine

Organic materials which show room-temperature phosphorescence (RTP) are of interest for many applications including chemical qubits which are the core units of a quantum information systems, organic light emitting diodes, chemical sensors. In contrast to triplet emitters based on noble metals (e.g. Ir, Rh), quantum yields of RTP of noble-atom-free organic emitters are much lower than unity. In this work, we report on a new approach to conformer-induced RTP enhancement of organic triplet emitters. The synthesis, thermal, photophysical, charge-transporting and oxygen sensing properties of the derivative of phenothiazine and triazatriazatruxene in which phenothiazine moieties are linked to nitrogen atoms of triazatriazatruxene via C-2 positions are presented. This compound exhibit stable RTP with a quantum yield of 54% which is more than six times higher than that of a reference material. For 1% solid solution of the compound in Zeonex, the ratio of intensity of RTP observed under vacuum and fluorescence intensity recorded in air reached the value of 19 which allows quantitative detection of oxygen with the high Stern-Volmer quenching constant of 7.83 × 10−3 ppm−1. The observed change of emission colour depending on the oxygen concentration can be used for the simple detection of oxygen by human eye.

Multiobjective Inverse Design of Solid-State Quantum Emitter Single-Photon Sources

Single solid-state quantum emitters offer considerable potential for the implementation of sources of single indistinguishable photons, which are central to many photonic quantum information systems. Nanophotonic geometry optimization with multiple performance metrics is imperative to convert a bare quantum emitter into a single-photon source that approaches the necessary levels of purity, indistinguishability, and brightness for quantum photonics. We present an inverse design methodology that simultaneously targets two important figures-of-merit for high-performance quantum light sources: the Purcell radiative rate enhancement and the coupling efficiency into a desired light collection channel. We explicitly address geometry-dependent power emission, a critical but often overlooked aspect of gradient-based optimization of quantum emitter single-photon sources. We illustrate the efficacy of our method through the design of a single-photon source based on a quantum emitter in a GaAs nanophotonic structure that provides a Purcell factor Fp = 21 with a 94% waveguide coupling efficiency, while respecting a geometric constraint to minimize emitter decoherence caused by etched sidewalls. Our results indicate that multiobjective inverse design can yield competitive performance with more favorable trade-offs than conventional approaches based on a pre-established waveguide or cavity geometries.

Few-cycle vacuum squeezing in nanophotonics.

One of the most fundamental quantum states of light is the squeezed vacuum, in which noise in one of the quadratures is less than the standard quantum noise limit. In nanophotonics, it remains challenging to generate, manipulate, and measure such a quantum state with the performance required for a wide range of scalable quantum information systems. Here, we report the development of a lithium niobate-based nanophotonic platform to demonstrate the generation and all-optical measurement of squeezed states on the same chip. The generated squeezed states span more than 25 terahertz of bandwidth supporting just a few optical cycles. The measured 4.9 decibels of squeezing surpass the requirements for a wide range of quantum information systems, demonstrating a practical path toward scalable ultrafast quantum nanophotonics.

Implement quantum tomography of polarization-entangled states via nondiffractive metasurfaces

Traditional optical elements, such as waveplates and polarization beam splitters, are essential for quantum state tomography (QST). Yet, their bulky size and heavy weight are prejudicial for miniaturizing quantum information systems. Here, we introduce nondiffractive silicon metasurfaces with high transmission efficiency to replace the traditional optical elements for QST of polarization-entangled states. Two identical silicon metasurfaces are employed, and each metasurface comprises four independent districts on a micrometer scale. The unit cell of each district consists of two silicon nanopillars with different geometrical sizes and orientation angles, and the interference of the scattered waves from the nanopillars leads to a single output beam from the district with a specific polarization state with a transmission efficiency above 92%. When the two-photon polarization-entangled state shines on different districts of two metasurfaces, each photon of the photon pair interacts with the local nanopillars within the district, and the two-photon state is projected onto 16 polarization bases for state reconstruction. We experimentally demonstrate the reconstruction of four input Bell states with high fidelities. This approach significantly reduces the number of conventional optical components in the QST process and is inspiring for advancing quantum information technology.

Focus on software, data acquisition, and instrumentation

Focus on software, data acquisition, and instrumentation

Pathway toward Optical Cycling and Laser Cooling of Functionalized Arenes.

Rapid and repeated photon cycling has enabled precision metrology and the development of quantum information systems using atoms and simple molecules. Extending optical cycling to structurally complex molecules would provide new capabilities in these areas, as well as in ultracold chemistry. Increased molecular complexity, however, makes realizing closed optical transitions more difficult. Building on already established strong optical cycling of diatomic, linear triatomic, and symmetric top molecules, recent work has pointed the way to cycling of larger molecules, including phenoxides. The paradigm for these systems is an optical cycling center bonded to a molecular ligand. Theory has suggested that cycling may be extended to even larger ligands, like naphthalene, pyrene, and coronene. Herein, we study optical excitation and fluorescent vibrational branching of CaO-[Formula: see text], SrO-[Formula: see text], and CaO-[Formula: see text] and find only weak decay to excited vibrational states, indicating a promising path to full quantum control and laser cooling of large arene-based molecules.

Investigating machine learning solutions for a 256 channel TCSPC camera with sub-70 ps single photon timing per channel at data rates >10 Gbps

The development of a Time Correlated Single Photon Counting (TCSPC) camera with 256 channels has enabled several applications where single photon sensitivity is crucial, such as LiDAR, Fluorescent Lifetime IMaging (FLIM) and quantum information systems. The microchannel plate-based Multi-Anode Photo-Multiplier Tube (MAPMT) is a 16 × 16 array of 1.656 mm pitch pixels with an active anode area of 26.5 × 26.5 mm2. Each pixel can time single photons with an accuracy of 60 ps rms at a maximum photon rate of 480 KHz.The timing electronics are capable of measuring 120 Mcps, producing huge volumes of data for processing, in the region of 10 Gbps per detector. Limitations in algorithmic data analysis techniques are critical for this application, hence this paper demonstrates a machine learning (ML) model which can determine the photon event coordinates with the objective of processing each one photon per 10 μs. The model applies calibrations for the detector and electronics such as amplitude walk, and charge measurement and channel to channel threshold variation. Optimisation of the model is detailed within the paper, including training hyperparameters, the clustering of coincident events and compression of the model through pruning techniques.The ML model is trained and tested on a simulation of the microchannel plate (MCP) PMT with timing electronics configured for use as a TCSPC camera, utilising charge sharing techniques to further improve the spatial resolution of the detector. Further objectives of the research are to test the model on detector data, allowing assessment on the variance of accuracy between simulated and real data. Beyond this, assessment of the performance of this approach compared to algorithmic approaches and introduction of statistical reasoning of the robustness of the model will be completed.

Tomography of Optical Single-Qubit Quantum Memory

Optical quantum memory is one of the basic elements of quantum information systems. However, the possibilities of its application in such systems sometimes can hardly be estimated by existing methods for its characterization. In this work, the tomography of quantum memory has been implemented as a quantum process in a logical basis. It has been shown that the implemented quantum memory scheme for polarization photon qubits with a high accuracy corresponds to the identity transformation and is promising for application in quantum communication and quantum computing.

Data-Driven and Multiscale Modeling of DNA-Templated Dye Aggregates.

Dye aggregates are of interest for excitonic applications, including biomedical imaging, organic photovoltaics, and quantum information systems. Dyes with large transition dipole moments () are necessary to optimize coupling within dye aggregates. Extinction coefficients () can be used to determine the of dyes, and so dyes with a large (>150,000 M−1cm−1) should be engineered or identified. However, dye properties leading to a large are not fully understood, and low-throughput methods of dye screening, such as experimental measurements or density functional theory (DFT) calculations, can be time-consuming. In order to screen large datasets of molecules for desirable properties (i.e., large and ), a computational workflow was established using machine learning (ML), DFT, time-dependent (TD-) DFT, and molecular dynamics (MD). ML models were developed through training and validation on a dataset of 8802 dyes using structural features. A Classifier was developed with an accuracy of 97% and a Regressor was constructed with an of above 0.9, comparing between experiment and ML prediction. Using the Regressor, the values of over 18,000 dyes were predicted. The top 100 dyes were further screened using DFT and TD-DFT to identify 15 dyes with a relative to a reference dye, pentamethine indocyanine dye Cy5. Two benchmark MD simulations were performed on Cy5 and Cy5.5 dimers, and it was found that MD could accurately capture experimental results. The results of this study exhibit that our computational workflow for identifying dyes with a large for excitonic applications is effective and can be used as a tool to develop new dyes for excitonic applications.

Synthesis of Eu(HCOO)3 and [formula omitted] crystals and observation of their 5D0→ 7F0 transition for quantum information systems

Two stoichiometric metal-organic frameworks containing Eu3+ cations are probed as candidates for photon-based quantum information storage. Synthesis procedures for growing 0.2 mm, rod-shaped Eu(HCOO)3 and 1–3 mm, rhombohedral Eu(HCOO)3⋅(HCONH2)2 single crystals are presented with visible precipitation as soon as 1 h into heating for Eu(HCOO)3 and 24 h for Eu(HCOO)3⋅(HCONH2)2. Room temperature and 1.4 K photoluminescence measurements of the 5D0→ 7FJ transitions of Eu3+ are analyzed for both compounds. Comparisons of peak width and intensity are discussed along with the notable first report for both of the 5D0→ 7F0 transition, the hyperfine structure of which has potential use in quantum memory applications. The air instability of Eu(HCOO)3⋅(HCONH2)2 and the transformation of its photoluminescence properties are discussed.

Complete Bell state measurement of diamond nuclear spins under a complete spatial symmetry at zero magnetic field

The symmetry of the space where a spin qubit resides plays an essential role in the manipulation of quantum entanglement, which governs the performance of quantum information systems. Application of a magnetic field, which is usually necessary for spin manipulation and readout, inevitably breaks the spatial symmetry to induce competition among quantization axes between internal and external fields, thus limiting the purity of the entanglement. If we could manipulate and readout entanglement under a zero magnetic field, we would be able to avoid the competition among quantization axes to achieve ideally high fidelity. We here demonstrate the complete Bell state measurement, which is a core element of quantum processing, of two carbon nuclear spins in the vicinity of a diamond nitrogen-vacancy center. The demonstration was made possible by holonomic entanglement manipulations based on the geometric phase with a polarized microwave under a zero magnetic field, where the quantization axis is uniquely defined by the hyperfine field. The demonstrated scheme allows high-fidelity entanglement processing even when magnetic fields cannot be applied to the integration of superconducting and spin qubits, thereby paving the way for building fault-tolerant distributed quantum computers and quantum repeater networks.

Single electrons on solid neon as a solid-state qubit platform.

Progress towards the realization of quantum computers requires persistent advances in their constituent building blocks-qubits. Novel qubit platforms that simultaneously embody long coherence, fast operation and large scalability offer compelling advantages in the construction of quantum computers and many other quantum information systems1-3. Electrons, ubiquitous elementary particles of non-zero charge, spin and mass, have commonly been perceived as paradigmatic local quantum information carriers. Despite superior controllability and configurability, their practical performance as qubits through either motional or spin states depends critically on their material environment3-5. Here we report our experimental realization of a qubit platform based on isolated single electrons trapped on an ultraclean solid neon surface in vacuum6-13. By integrating an electron trap in a circuit quantum electrodynamics architecture14-20, we achieve strong coupling between the motional states of a single electron and a single microwave photon in an on-chip superconducting resonator. Qubit gate operations and dispersive readout are implemented to measure the energy relaxation time T1 of 15 μs and phase coherence time T2 over 200 ns. These results indicate that the electron-on-solid-neon qubit already performs near the state of the art for a charge qubit21.