EPJ Quantum Technology最新文献

Scalable solutions are essential to achieving the long-term goal of building a fault-tolerant quantum computer and energy-power consumption are fundamental limiting factors for this target. Among the available types of silicon qubits, this work focuses on Flip-Flop (FF) qubits. Energy consumption and power requirements are estimated for a square array of qubits that hosts the logical qubit. The logical qubit is implemented using the rotated Surface Code (SC) for Quantum Error Correction (QEC). By using a universal set of quantum gates, the energy usage, time and power requirements for a SC cycle are estimated based on noise level, code distance and control levels. These estimates are used to provide insights into the main scaling-up challenges for quantum computer development. This is achieved by extending a thermal model that includes energy contributions from both the cryogenic components (such as the qubit array, the cryogenic control electronics, and the cryostat) and the room temperature (RT) section (RT electronics and heat dissipation systems). The maximum numbers of physical and logical qubits are provided, as well as power consumption across the different temperature sections.

Free-induction-decay (FID) magnetometer is highly suitable for precise magnetic field sensing in unshielded environments with the benefit of exceptional accuracy and large dynamic range. The sensitivity of the FID magnetometer is directly influenced by the signal-to-noise ratio, making it critical to enhance the amplitude of the FID signal. In this study, we propose a FID magnetometer based on synchronous optical pumping and RF pulse modulation. A comprehensive theoretical description of the magnetometer is introduced, followed by simulation and experiment that compare the proposed modulation method with the synchronous optical pumping modulation method and the RF pulse modulation method. The results show that the synchronous optical pumping and RF pulse modulation achieves the enhancement of the FID signal and improves the magnetometer sensitivity. Furthermore, the dead zone of the magnetometer is reduced to the direction of the probe beam. This work is significant for further development of optically pumped magnetometers and provides a new scheme for their applications in unshielded environments.

In this article, we investigate the development of the European field of Quantum Technology education, by drawing on the framework of activity theory (AT), most frequently employed in the social sciences. Focusing on the QTEdu CSA, an impactful European project intended to unite stakeholders in QT education, we study the evolution of 11 pilot projects, cross-cutting education for members of the public, high schools, universities, and industry. The pilots are modelled as activities, drawing on data from 402 online profiles, 33 written reports, and 13 interviews conducted with pilot coordinators and members. Through identifying their elements in the language of activity theory, we examine the structure of the community, and the interactions between the individuals, which may have contributed to the development of QT education in Europe. To do so, we use activity theoretic concepts such as contradiction and expansive learning, offering a practical explanation for using AT to model communities, such that it may benefit future research studying community-based transformations in STEM education.

Quantum dialogue (QD) is a term of quantum cryptography, which can fulfill the secure exchange of two parties’ private information in an open environment. Up to now, there have been a lot of QD protocols. Many have several common components and activities, such as encoding photons coming forth with auxiliary photons and back, one party or both performing unitary operations on encoding photons, two times of security check, and both parties’ private data being decoded chronologically from encoding photons. This work proposes a brand-new QD model, whose quantum transmission is unidirectional with only one security check and decoding of both parties’ secrets are simultaneous. Equally important is neither unitary operations nor auxiliary photons being used. Consequently, such a QD can substantially reduce costs and increase efficiency, thus entitled fast quantum dialogue (FQD). The presented FQD protocol is analysed with safety and without information leakage. Moreover, its information-theoretical efficiency is 88.89%, much higher than the current maximum 66.67%. So, it offers us a better alternative for QD.

As a particular area of quantum security multiparty computation, quantum secure multiparty summation plays a critical role in modern cryptography. It is widely known that most of the existing quantum summation protocols are based on an honest or semi-honest third party (TP). However, the introduced TP makes the protocol difficult to implement in practice, as it may face a single-point-of-failure attack on TP. Although some TP-free protocols are proposed to mitigate this risk, the increased cost of communication reduces its efficiency. To address these issues, a novel quantum-secure multiparty summation protocol based on a cooperative random number distribution mechanism (QMS-CRM) is proposed in this paper for the first time. During it, this mechanism is designed using Shamir’s secret sharing scheme. Furthermore, this approach eliminates the requirement for random number exchange between participants without the help of TP, enhancing the efficiency of the protocol. The security analysis demonstrates that the proposed protocol can resist both external attacks and collusion attacks by up to (n - 2) participants. Finally, we simulated the protocol on the IBM Quantum Cloud platform, confirming its feasibility.

Accurate measurements with implications in many branches of physics have been accessed using conventional techniques in Penning traps within a temperature regime where each eigenmotion of a charged particle is still a classical harmonic oscillator. Cooling the particle directly or indirectly with lasers allows reaching the quantum regime of each oscillator, controlling subtle effects in the precision frontier by detecting photons instead of electric currents. In this paper, we present a new in-vacuum optical system designed to detect 397-nm fluorescence photons from individual calcium ions and Coulomb crystals in a 7-T Penning trap. Based on the outcome of computer simulations, our design shows diffraction-limited performance. The system has been characterized using a single laser-cooled ion as a point-like source, reaching a final resolution of 3.69(3) μm and 2.75(3) μm for the trap’s axial and radial directions, respectively, after correcting aberrations.

The National Aeronautics and Space Administration (NASA) develops a broad range of technologies to support space-based quantum sensing and communications, uses the space environment to study fundamental quantum processes to advance our knowledge of physics, and develops algorithms to attack complex science problems that might be solved using quantum computing. This paper describes quantum sensors that NASA has flown on space missions, investments that NASA is making to develop quantum sensors, and possible approaches to employ quantum sensing to study the attributes of distant stars and planets, the Sun, Earth, and fundamental properties of matter.

Preparing quantum state remotely plays an important role in quantum communication network. Most of the previous protocols for parallel preparation quantum state remotely only consider parallel remote preparation of arbitrary single-qubit states. In this paper, we propose a protocol for parallel remote preparation of two-qubit hybrid states with a two-photon hyperentangled state. The arbitrary two-qubit hybrid states encoded in spatial-mode, frequency, polarization and time-bin degrees of freedom(DOFs) can be remotely prepared via hyperentangled state and optical elements. Moreover, we discuss parallel remote preparation of two-qubit hybrid states via partially hyperentangled state. The protocol for parallel remote preparation of two-qubit hybrid states has the advantage of having high channel capacity for long distance quantum communication by using hyperentangled state simultaneously entangled in spatial-mode, frequency, polarization and time-bin DOFs as the quantum channel.

We propose a new approach to utilize quantum computers for binary linear programming (BLP), which can be extended to general integer linear programs (ILP). Quantum optimization algorithms, hybrid or quantum-only, are currently general purpose, standalone solvers for ILP. However, to consider them practically useful, we expect them to overperform the current state of the art classical solvers. That expectation is unfair to quantum algorithms: in classical ILP solvers, after many decades of evolution, many different algorithms work together as a robust machine to get the best result. This is the approach we would like to follow now with our quantum ‘solver’ solutions. In this study we wrap any suitable quantum optimization algorithm into a quantum informed classical constraint generation framework. First we relax our problem by dropping all constraints and encode it into an Ising Hamiltonian for the quantum optimization subroutine. Then, by sampling from the solution state of the subroutine, we obtain information about constraint violations in the initial problem, from which we decide which coupling terms we need to introduce to the Hamiltonian. The coupling terms correspond to the constraints of the initial binary linear program. Then we optimize over the new Hamiltonian again, until we reach a feasible solution, or other stopping conditions hold. Since one can decide how many constraints they add to the Hamiltonian in a single step, our algorithm is at least as efficient as the (hybrid) quantum optimization algorithm it wraps. We support our claim with results on small scale minimum cost exact cover problem instances.

Exchange-only quantum computation is a version of spin-based quantum computation that entirely avoids the difficulty of controlling individual spins by a magnetic field and instead functions by sequences of exchange pulses. The challenge for exchange-only quantum computation is to find short sequences that generate the required logical quantum gates. A reduction of the total gate time of such synthesized quantum gates can help to minimize the effects of decoherence and control errors during the gate operation and thus increase the total gate fidelity. We apply reinforcement learning to the optimization of exchange-gate sequences realizing the CNOT and CZ two-qubit gates which lend themselves to the construction of universal gate sets for quantum computation. We obtain a significant improvement regarding the total gate time compared to previously published results.