Quantum Information Technology Research Articles

Traceable localization enables accurate integration of quantum emitters and photonic structures with high yield.

In a popular integration process for quantum information technologies, localization microscopy of quantum emitters guides lithographic placement of photonic structures. However, a complex coupling of microscopy and lithography errors degrades registration accuracy, severely limiting device performance and process yield. We introduce a methodology to solve this widespread but poorly understood problem. A new foundation of traceable localization enables rapid characterization of lithographic standards and comprehensive calibration of cryogenic microscopes, revealing and correcting latent systematic effects. Of particular concern, we discover that scale factor deviation and complex optical distortion couple to dominate registration errors. These novel results parameterize a process model for integrating quantum dots and bullseye resonators, predicting higher yield by orders of magnitude, depending on the Purcell factor threshold as a quantum performance metric. Our foundational methodology is a key enabler of the lab-to-fab transition of quantum information technologies and has broader implications to cryogenic and correlative microscopy.

Quantum entanglement and interference at 3 μm.

Given the important advantages of the mid-infrared optical range (2.5 to 25 μm) for biomedical sensing, optical communications, and molecular spectroscopy, extending quantum information technology to this region is highly attractive. However, the development of mid-infrared quantum information technology is still in its infancy. Here, we report on the generation of a time-energy entangled photon pair in the mid-infrared wavelength band. By using frequency upconversion detection technology, we observe the two-photon Hong-Ou-Mandel interference and demonstrate the time-energy entanglement between twin photons at 3082 nm via the Franson-type interferometer, verifying the indistinguishability and nonlocality of the photons. This work is very promising for future applications of optical quantum technology in the mid-infrared band, which will bring more opportunities in the fields of quantum communication, precision sensing, and imaging.

Theoretical investigation of multiplexed quantum light source in fiber ring cavities with oscillating dispersion

Correlated photon pairs are the core resources for photonic quantum information technology. Multiplexed quantum light sources can appreciably improve the efficiency of quantum information processing. Here, we develop a coupled-mode mean-field model and its corresponding semiclassical theory analysis to investigate the multiple parametric-gain sidebands in dispersion-oscillation fiber-ring cavities. We present a cycle transfer matrix method to give the analytic expressions for parametric gain. From this, we can reach a physical insight, that is additional degree of freedom introduced by the modulation along fiber length is responsible for the multiple parametric-gain sidebands, where the underlying mechanism is the quasi-phase matching of four-wave mixing. Two twin signal and idler photons generated from parametric-gain sidebands are appreciably of frequency and temporal correlation, revealing promising applications in frequency-multiplexed photon pair sources. When we construct an optical cavity with spliced single mode fiber and dispersion shifted fibers, numerous parametric-gain sidebands grow in the vicinity of zero group-velocity-dispersion wavelengths of two fibers, i.e., 1310 nm and 1550 nm, both corresponding to low transmission loss windows of fibers. Therefore, frequency-multiplexed quantum light sources established on dispersion-oscillation fiber-ring cavities have the advantages in economy, remote transmission, scalability and compatibility with fiber communication network. Our work offers inspiration for the development of a multiplexed quantum light source.

Multipartite Entanglement: A Journey through Geometry.

Genuine multipartite entanglement is crucial for quantum information and related technologies, but quantifying it has been a long-standing challenge. Most proposed measures do not meet the "genuine" requirement, making them unsuitable for many applications. In this work, we propose a journey toward addressing this issue by introducing an unexpected relation between multipartite entanglement and hypervolume of geometric simplices, leading to a tetrahedron measure of quadripartite entanglement. By comparing the entanglement ranking of two highly entangled four-qubit states, we show that the tetrahedron measure relies on the degree of permutation invariance among parties within the quantum system. We demonstrate potential future applications of our measure in the context of quantum information scrambling within many-body systems.

Quantum confinement effects on the structural and optical properties of nanostructured tin oxide powder

Nanostructured Tin oxide powders, prepared by chemical precipitation method, exhibit interesting structural and optical properties at nanoscale dimensions. Structural characterization confirmed the formation of pure nanostructured SnO2 powders with average crystalline grain size of 54.4[Formula: see text]nm calculated with relative uncertainty of 1.62%. The optical properties of nanoSnO2 powder performed by using transmittance and photoluminescence measurements reveal high transparency and multi-photon emissions in visible and ultraviolet regions. The different photon emissions are attributed to radiative transitions via oxygen vacancies, Sn interstitials, Sn substitutional and dangling bonds. The lower wavelength value corresponded to the absorption edge peak indicating the good quantum confinement of nanostructured SnO2 powder. The larger optical band gap, calculated through transmittance measurements, confirms the quantum confinement effects. The presence of quantum confinement and native point defects in nanostructured SnO2 powders can contribute to enhancing photon emissions process. This result may offer inherent advantages over conventional materials for photonic quantum information technology. The sustained photon emission at room temperature, indicates that SnO2 nanoparticles could be useful in room temperature quantum computing and can maintain the delicate quantum states required for computation at higher temperatures.

Highly entangled polyradical nanographene with coexisting strong correlation and topological frustration.

Open-shell nanographenes exhibit unconventional π-magnetism arising from topological frustration or strong electron-electron interaction. However, conventional design approaches are typically limited to a single magnetic origin, which can restrict the number of correlated spins or the type of magnetic ordering in open-shell nanographenes. Here we present a design strategy that combines topological frustration and electron-electron interactions to fabricate a large fully fused 'butterfly'-shaped tetraradical nanographene on Au(111). We employ bond-resolved scanning tunnelling microscopy and spin-excitation spectroscopy to resolve the molecular backbone and reveal the strongly correlated open-shell character, respectively. This nanographene contains four unpaired electrons with both ferromagnetic and anti-ferromagnetic interactions, harbouring a many-body singlet ground state and strong multi-spin entanglement, which is well described by many-body calculations. Furthermore, we study the magnetic properties and spin states in the nanographene using a nickelocene magnetic probe. The ability to imprint and characterize many-body strongly correlated spins in polyradical nanographenes paves the way for future advancements in quantum information technologies.

Single-photon generation from a neodymium ion in optical fiber at room temperature

The realization of single-photon generation is important for implementing various quantum information technologies. The use of rare-earth ions in an optical fiber is a promising single-photon generation method due to its ability to operate at room temperature as well as the low cost involved. Neodymium ions are especially interesting because the ions are one of the most commercially affordable rare-earth materials in the current industry. The neodymium ion also has the advantage of having a rich energy level structure, which offers several possible wavelengths for emitted single photons from visible to near-telecommunication wavelengths. In this paper, we experimentally demonstrated single-photon generation using an isolated single neodymium ion in tapered silica fiber at room temperature. Our results have significant implications as a platform for low-cost wavelength-selectable single-photon sources and photonic quantum applications.

Long‐range quantum energy teleportation and distribution on a hyperbolic quantum network

AbstractTeleporting energy to remote locations is new challenge for quantum information science and technology. Developing a method for transferring local energy in laboratory systems to remote locations will enable non‐trivial energy flows in quantum networks. From the perspective of quantum information engineering, we propose a method for distributing local energy to a large number of remote nodes using hyperbolic geometry. Hyperbolic networks are suitable for energy allocation in large quantum networks since the number of nodes grows exponentially. To realise long‐range quantum energy teleportation (QET), we propose a hybrid method of quantum state telepotation and QET. By transmitting local quantum information through quantum teleportation and performing conditional operations on that information, QET can theoretically be realized independent of geographical distance. The method we present will provide new insights into new applications of future large‐scale quantum networks and potential applications of quantum physics to information engineering.

Building and characterizing a stylus ion-trap system

Cold trapped ions can be excellent sensors for ultra-precision detection of physical quantities, which strongly depends on the measurement situation at hand. The stylus ion trap, formed by two concentric cylinders over a ground plane, holds the promise of relatively simple structure and larger solid angle for optical access and fluorescence collection in comparison with the conventional ion traps. Here we report our fabrication and characterization of the first stylus ion trap constructed in China, aiming for studying quantum optics and sensing weak electric fields in the future. We have observed the stable confinement of the ion in the trapping potential for more than two hours and measured the heating rate of the trap to be dε/dt = 7.10 ± 0.13 meV/s by the Doppler recooling method. Our work starts a way to building practical quantum sensors with high efficiency of optical collection and with ultimate goal for contributing to future quantum information technology.

A Kind of (n,t)Threshold Quantum State Sharing Scheme Based on Chinese Reminder Theorem

Secret sharing is a key technology of data confidentiality, where one can distribute a secret among agents, and only the authorized agents can recover the original secret. Quantum information technology, including quantum communication, quantum computing can break through the bottlenecks of classical technology in information security and computing speed, based on quantum mechanics, such as quantum superposition, quantum uncertainty, quantum no-cloning and quantum entanglement. By combining quantum technology with classic secret sharing, the concept of quantum state sharing was presented. In this manuscript, a novel kind of (n,t) threshold quantum state sharing scheme is proposed, where the selected t agents among n agents can cooperate to reconstruct the target secret state. For implementing this scheme, the Chinese reminder theorem is introduced during the processing of the secret key distribution. In addition, to show the proposed scheme clearly, a concrete (5,3) example is given. Furthermore, the proof of the correctness of the scheme is shown. Our scheme will improve the development the quantum secret sharing and open up exploring the application of quantum information technology

Cryogenic Resonant Amplifier for Electron-on-Helium Image Charge Readout

AbstractAn electron-on-helium qubit is a promising physical platform for quantum information technologies. Among all the “blueprints” for the qubit realization, a hybrid Rydberg-spin qubit seems to be a promising one toward quantum computing using electron spins. The main technological challenge on the way to such qubits is a detection of fA range image current induced by a Rydberg transition of a single electron. To address this problem, we aim to use a tank LC-circuit in conjunction with a high-impedance and low power dissipation cryogenic amplifier. Here, we report our progress toward realization of a resonant image current detector with a homemade cryogenic amplifier based on FHX13LG HEMT. We present a detailed characterization of the transistor at room and cryogenic temperatures, as well as details of the amplifier design and performance. At the power dissipation level of amplifier well below 100 μW, the measured voltage and current noise level are $$0.6~{\hbox {nV}}/\sqrt{\textrm{Hz}}$$ 0.6 nV / Hz and below 1.5 fA/$$\sqrt{\textrm{Hz}}$$ Hz , respectively. Based on the actual image current measurements of the Rydberg transition in a many-electron system on liquid helium, we estimate an SNR = 8 with a measurement bandwidth 1 Hz for the detection of a single-electron transition, providing the noise level at the output is solely determined by the noise of the amplifier.

Where Atomically Precise Catalysts, Optoelectronic Devices, and Quantum Information Technology Intersect: Atomic Layer Deposition

Where Atomically Precise Catalysts, Optoelectronic Devices, and Quantum Information Technology Intersect: Atomic Layer Deposition

Wireless quantum key distribution at terahertz frequencies: Opportunities and challenges

AbstractQuantum key distribution (QKD) is one of the major applications of quantum information technology. It can provide ultra‐secure key distribution with security guaranteed by the laws of quantum physics. Quantum key distribution is necessary to protect data transmission from quantum computing attacks in future communication networks. The laws of quantum mechanics dictate that as opposed to microwave frequencies, quantum coherence is preserved at room temperatures for terahertz (THz) frequencies. This makes the THz band a promising solution for room‐temperature QKD implementation in future wireless communication networks. The authors present the principles of continuous variable QKD (CV‐QKD) systems and review the latest developments in the design and analysis of CV‐QKD systems operating at microwave and THz frequencies. The authors also discuss how multiple‐input multiple‐output transmission can be incorporated into the quantum communications framework to improve the secret key rates and increase the coverage distances of the THz CV‐QKD system. Furthermore, major hardware challenges that must be surmounted to practically realise THz CV‐QKD systems are highlighted.

Two-dimensional few-atom noble gas clusters in a graphene sandwich.

The van der Waals atomic solids of noble gases on metals at cryogenic temperatures were the first experimental examples of two-dimensional systems. Recently, such structures have also been created on surfaces under encapsulation by graphene, allowing studies at elevated temperatures through scanning tunnelling microscopy. However, for this technique, the encapsulation layer often obscures the arrangement of the noble gas atoms. Here we create Kr and Xe clusters in between two suspended graphene layers, and uncover their atomic structure through transmission electron microscopy. We show that small crystals (N < 9) arrange on the basis of the simple non-directional van der Waals interaction. Larger crystals show some deviations, possibly enabled by deformations in the encapsulating graphene lattice. We further discuss the dynamics of the clusters within the graphene sandwich, and show that although all the Xe clusters with up to N ≈ 100 remain solid, Kr clusters with already N ≈ 16 turn occasionally fluid under our experimental conditions (under a pressure of ~0.3 GPa). This study opens a way for the so-far unexplored frontier of encapsulated two-dimensional van der Waals solids with exciting possibilities for fundamental condensed-matter physics research and possible applications in quantum information technology.

Shortcut-based generation of transmon-magnon entangled states

Optimized generation of entangled states between solid-state qubits is of fundamental significance to quantum information science and technology. Here, we develop an effective scheme to fast and robustly create the entangled states in a hybrid system containing a superconducting transmon qubit and a spin magnon of yttrium iron garnet. The transmon qubit and the magnon system are coupled via a microwave cavity field. Within the framework of invariant-based shortcuts to adiabaticity, the transmon-magnon entangled states can be rapidly induced by engineering the Rabi couplings between the cavity mode and transmon (magnon) with constant amplitudes. Compared with a non-shortcut counterpart, the shortcut-based operations of interest not only considerably shorten the generation time, but also greatly mitigate the decoherence effects. Furthermore, the fast dynamics is well insensitive to the control deviation of Rabi couplings. Thus our approach could lead to advances in information processing and state engineering with composite systems.

The Rise of Quantum Information and Communication Technologies

Today, we are already using several-component devices and systems based on the technologies developed during the first quantum revolution. Examples include microchips for servers, laptops and smartphones, medical imaging devices, LED, lasers, etc. Now, a second quantum revolution is progressing fast, exploiting technological advances for the ability to engineer and manipulate other quantum phenomena such as superposition, entanglement and measurement. As a matter of fact, there is an impressive increase in research and development activities, innovation, public and private investments in a new wave of quantum services and applications. In this scenario, quantum information and communication technologies (QICTs) can be defined as a set of technological components, devices, systems and methods for elaborating, storing and transmitting/sharing quantum information. This paper addresses the challenges and opportunities enabling the rise of QICTs. In order to provide a concrete example, the paper describes an overview of the European project EQUO (European Quantum ecOsystems) dealing with ongoing innovation activities in the QICT avenue; in fact, EQUO aims at developing and demonstrating the feasibility of QKD (quantum key distribution) networks and their related integration in current telecommunications infrastructures towards the quantum internet.

Deterministic Conversion of Hyperentangled States with Error‐Heralded Quantum Units

AbstractIn the paper, the possibility of two complete conversions is investigated, one is from the two‐photon hyperentangled Knill–Laflamme–Milburn (KLM) state to hyperentangled Bell states, the other is from three‐photon KLM state to the hyperentangled Greenberger–Horne–Zeilinger states, for photonic systems hyper‐encoded in polarization and spatial degrees of freedom assisted by error‐heralded quantum units (EHQUs). The system inhomogeneity and/or the imperfect photon scattering often restrict the performance of effective conversions of two types of hyperentangled states, and result in the reductions of the fidelity and the efficiency in tangible quantum information technologies. The polarization EHQU and spatial EHQU are two critical tools for actualizing two hyperentangled conversions in a heralded way, as the errors stemming from the system inhomogeneity and practically imperfect scattering are converted into efficacious responses of the detectors in our protocols. Thus, the fidelities of these conversion cases keep unchanged and have close to unity fidelities, which deepen the understanding of the properties of hyperentanglement.

Observation and manipulation of quantum interference in a superconducting Kerr parametric oscillator

Quantum tunneling is the phenomenon that makes superconducting circuits “quantum”. Recently, there has been a renewed interest in using quantum tunneling in phase space of a Kerr parametric oscillator as a resource for quantum information processing. Here, we report a direct observation of quantum interference induced by such tunneling and its dynamics in a planar superconducting circuit through Wigner tomography. We experimentally elucidate all essential properties of this quantum interference, such as mapping from Fock states to cat states, a temporal oscillation due to the pump detuning, as well as its characteristic Rabi oscillations and Ramsey fringes. Finally, we perform gate operations as manipulations of the observed quantum interference. Our findings lay the groundwork for further studies on quantum properties of superconducting Kerr parametric oscillators and their use in quantum information technologies.

Quantum key distribution using deterministic single-photon sources over a field-installed fibre link

Quantum-dot-based single-photon sources are key assets for quantum information technology, supplying on-demand scalable quantum resources for computing and communication. However, long-lasting issues such as limited long-term stability and source brightness have traditionally impeded their adoption in real-world applications. Here, we realize a quantum key distribution field trial using true single photons across an 18-km-long dark fibre, located in the Copenhagen metropolitan area, using an optimized, state-of-the-art, quantum-dot single-photon source frequency-converted to the telecom wavelength. A secret key generation rate of > 2 kbits/s realized over a 9.6 dB channel loss is achieved with a polarization-encoded BB84 scheme, showing remarkable stability for more than 24 hours of continuous operation. Our results highlight the maturity of deterministic single-photon source technology while paving the way for advanced single-photon-based communication protocols, including fully device-independent quantum key distribution, towards the goal of a quantum internet.

Quantum information technology: Current status and prospects

In the early decades of the 20th century, the inception of quantum mechanics catalyzed the first quantum revolution, resulting in groundbreaking technological advances, such as nuclear energy, semiconductors, lasers, nuclear magnetic resonance, superconductivity, and global satellite positioning systems. These innovations have promoted significant progress in material civilization, fundamentally changed the way of life and societal landscape of humanity. Since the 1990s, quantum control technology has made significant strides forward, ushering in a rapid evolution of quantum technologies, notably exemplified by quantum information science. This encompasses domains such as quantum communication, quantum computing, and quantum precision measurement, offering paradigm-shifting solutions for enhancing information transmission security, accelerating computational speed, and elevating measurement precision. These advances hold the potential to provide crucial underpinning for national security and the high-quality development of the national economy. The swift progression of quantum information technology heralds the advent of the second quantum revolution. Following nearly three decades of concerted efforts, China’s quantum information technology field as a whole has achieved a leap. Specifically, China presently assumes a prominent international role in both the research and practical application of quantum communication, leading the global domain in quantum computing, and achieving international preeminence or advanced standing across various facets of quantum precision measurement. Presently, it is imperative to conduct a comprehensive assessment of the developmental priorities in the realm of quantum information in China for the forthcoming 5 to 10 years, in alignment with national strategic priorities and the evolving landscape of international competition. This will enable the proactive establishment of next-generation information technology systems that are secure, efficient, autonomous, and controllable.