Quantum Space Research Articles

Advances in space quantum communications

Concerted efforts are underway to establish an infrastructure for a global quantum Internet to realise a spectrum of quantum technologies. This will enable more precise sensors, secure communications, and faster data processing. Quantum communications are a front-runner with quantum networks already implemented in several metropolitan areas. A number of recent proposals have modelled the use of space segments to overcome range limitations of purely terrestrial networks. Rapid progress in the design of quantum devices have enabled their deployment in space for in-orbit demonstrations. We review developments in this emerging area of space-based quantum technologies and provide a roadmap of key milestones towards a complete, global quantum networked landscape. Small satellites hold increasing promise to provide a cost effective coverage required to realise the quantum Internet. The state of art in small satellite missions is reviewed and the most current in-field demonstrations of quantum cryptography are collated. The important challenges in space quantum technologies that must be overcome and recent efforts to mitigate their effects are summarised. A perspective on future developments that would improve the performance of space quantum communications is included. The authors conclude with a discussion on fundamental physics experiments that could take advantage of a global, space-based quantum network.

Quantum gravity states, entanglement graphs and second-quantized tensor networks

In recent years, the import of quantum information techniques in quantum gravity opened new perspectives in the study of the microscopic structure of spacetime. We contribute to such a program by establishing a precise correspondence between the quantum information formalism of tensor networks (TN), in the case of projected entangled-pair states (PEPS) generalised to a second-quantized framework, and group field theory (GFT) states, and by showing how, in this quantum gravity approach, discrete spatial manifolds arise as entanglement patterns among quanta of space, having a dual representation in terms of graphs and simplicial complexes. We devote special attention to the implementation and consequences of the label independence of the graphs/networks, corresponding to the indistinguishability of the space quanta and representing a discrete counterpart of the diffeomorphism invariance of a consistent quantum gravity formalism. We also outline a relational setting to recover distinguishability of graph/network vertices at an effective and physical level, in a partial semi-classical limit of the theory.

Left-covariant differential calculi on GL̃q(2)

We define a new ${\mathbb Z}_2$-graded quantum (2+1)-space and show that the extended ${\mathbb Z}_2$-graded algebra of polynomials on this ${\mathbb Z}_2$-graded quantum space, denoted by ${\cal F}({\mathbb C}_q^{2\vert1})$, is a ${\mathbb Z}_2$-graded Hopf algebra. We construct a right-covariant differential calculus on ${\cal F}({\mathbb C}_q^{2\vert1})$ and define a ${\mathbb Z}_2$-graded quantum Weyl algebra and mention a few algebraic properties of this algebra. Finally, we explicitly construct the dual ${\mathbb Z}_2$-graded Hopf algebra of ${\cal F}({\mathbb C}_q^{2\vert1})$.

Quantum Composition and Improvisation

Quantum mechanical systems exist as superpositions of complementary states that collapse to classical, concrete states upon becoming entangled with the measurement apparatus of observer-participants. A musical composition and its performance constitute a quantum system. Historically, conventional musical notation has presented the appearance of a composition as a deterministic, concrete entity, with interpretation approached as an extrinsic act. This historical perspective inhabits a subspace of the available quantum space. A quantum musical system unifies the composition, instruments, situated performance and perception as a superposition of musical events that collapses to concrete musical events via the interactions and perceptions of performers and audience. A composer captures superposed musical events via implicit or explicit conditional event probabilities, and human and/or machine performers create music by collapsing interrelated probabilities to zeros and ones via observer-participancy.

Discrete phase space and continuous time relativistic quantum mechanics I: Planck oscillators and closed string-like circular orbits

The discrete phase space continuous time representation of relativistic quantum mechanics involving a characteristic length [Formula: see text] is investigated. Fundamental physical constants such as [Formula: see text], [Formula: see text], and [Formula: see text] are retained for most sections of the paper. The energy eigenvalue problem for the Planck oscillator is solved exactly in this framework. Discrete concircular orbits of constant energy are shown to be circles [Formula: see text] of radii [Formula: see text] within the discrete [Formula: see text]-dimensional phase plane. Moreover, the time evolution of these orbits sweep out world-sheet like geometrical entities [Formula: see text] and therefore appear as closed string-like geometrical configurations. The physical interpretation for these discrete orbits in phase space as degenerate, string-like phase cells is shown in a mathematically rigorous way. The existence of these closed concircular orbits in the arena of discrete phase space quantum mechanics, known for the non-singular nature of lower order expansion [Formula: see text] matrix terms, was known to exist but has not been fully explored until now. Finally, the discrete partial difference-differential Klein–Gordon equation is shown to be invariant under the continuous inhomogeneous orthogonal group [Formula: see text].

Quantum advantage for computations with limited space

Quantum computations promise the ability to solve problems intractable in the classical setting. Restricting the types of computations considered often allows to establish a provable theoretical advantage by quantum computations, and later demonstrate it experimentally. In this paper, we consider space-restricted computations, where input is a read-only memory and only one (qu)bit can be computed on. We show that $n$-bit symmetric Boolean functions can be implemented exactly through the use of quantum signal processing as restricted space quantum computations using $O(n^2)$ gates, but some of them may only be evaluated with probability $1/2 + O(n/\sqrt{2}^n)$ by analogously defined classical computations. We experimentally demonstrate computations of $3$-, $4$-, $5$-, and $6$-bit symmetric Boolean functions by quantum circuits, leveraging custom two-qubit gates, with algorithmic success probability exceeding the best possible classically. This establishes and experimentally verifies a different kind of quantum advantage -- one where quantum scrap space is more valuable than analogous classical space -- and calls for an in-depth exploration of space-time tradeoffs in quantum circuits.

Nonclassical atomic system dynamics time-dependently interacts with finite entangled pair coherent parametric converter cavity fields

We consider a time-dependent model that describes a qubit time-dependently interacting with a cavity containing finite entangled pair coherent parametric converter fields. The dynamics of some quantum phenomena, as: phase space information, quantum entanglement and squeezing, are explored by atomic Husimi function, atomic Wehrl entropy, variance, and entropy squeezing. The influences of the unitary qubit-cavity interaction, the difference between the two-mode photon numbers, the initial atomic coherence, and the time-dependent qubit location are investigated. It is found that the regularity, the amplitudes and the frequency of the quantum phenomena can be controlled by the physical parameters. For the initial atomic pure state, the qubit-cavity entanglement, the qubit phase space information, and atomic squeezing can be generated strongly compared to those of the initial atomic mixed state. The time-dependent location parameters enhance the generated quantum phenomena, and their effect can be enhanced by the parameters of the two-mode photon numbers and the initial atomic coherence.

Efficient Fourier space quantum dot k ⋅ p for wurtzite systems including smooth alloy profile and spatially varying elastic and dielectric constants

We present methods to calculate the electronic structure of wurtzite quantum dot systems with continuous alloy profiles within Fourier-space-based k⋅p theory. We incorporate spatially varying elastic and dielectric constants in strain and piezoelectric potential calculations. A method to incorporate smooth alloy profiles in all aspects of the calculations is presented. We demonstrate our methodology for the case of a 1-dimensional InGaN quantum dot array and show the importance of including these spatially varying parameters in the modeling of devices. We demonstrate that the convergence of the lowest bound state energies is for good approximation determined by the largest wave vector used in constructing the states. We also present a novel approach of coupling strain into the k⋅p Hamiltonian, greatly reducing the computational cost of generating the Hamiltonian.

Advances of relativity theory

Advances of relativity theory are in the replacement of the space-time model with time-invariant universal space that has a variable energy density. Every physical object with mass m and energy E is diminishing the energy density of space exactly for the amount of its energy. Lorentz factor has its origin in the variable density of universal space, we call it “superfluid quantum space”—SQS that is the primordial energy of the universe. Universal SQS is the absolute frame of reference for all observers as confirmed experimentally by the general positioning system, which demonstrates that the relative rate of clocks is valid for all observers. A planet's perihelion precession and the Sagnac effect are the results of the SQS dragging effect.

Momentum Space Quantum Monte Carlo on Twisted Bilayer GrapheneSupported by the RGC of Hong Kong SAR of China (Grant Nos. 17303019, 17301420, and AoE/P-701/20), the National Key Research and Development Program of China (Grant No. 2016YFA0300502), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB33000000 and XDB28000000), the National Natural Science Foundation of China (Grant

We report an implementation of the momentum space quantum Monte Carlo (QMC) method on the interaction model for the twisted bilayer graphene (TBG). The long-range Coulomb repulsion is treated exactly with the flat bands, spin and valley degrees of freedom of electrons taking into account. We prove the absence of the minus sign problem for QMC simulation when either the two valleys or the two spin degrees of freedom are considered. By taking the realistic parameters of the twist angle and interlayer tunnelings into the simulation, we benchmark the QMC data with the exact band gap obtained at the chiral limit, to reveal the insulating ground states at the charge neutrality point (CNP). Then, with the exact Green’s functions from QMC, we perform stochastic analytic continuation to obtain the first set of single-particle spectral function for the TBG model at CNP. Our momentum space QMC scheme therefore offers the controlled computation pathway for systematic investigation of the electronic states in realistic TBG model at various electron fillings.

A novel quantum inspired hybrid metaheuristic for dispatch of power system including solar photovoltaic generation

ABSTRACT This manuscript proposes a novel metaheuristic, which is an amalgamation of the quantum concept and the gravitational search particle swarm optimization technique. The inclusion of quantum concepts in the algorithm enhances its capability, as in quantum space there is no restriction on the movement of particle and the solution can be obtained with smaller population and faster convergence. An adaptive contraction expansion factor is also introduced which ensures better exploration of the algorithm. The technique is applied to solve the combined economic emission dispatch of a hybrid solar thermal unit operating in New Delhi, India for full and reduced solar radiation. To verify the effectiveness of the proposed technique, it is also applied to solve the combined economic emission dispatch of a 10 unit, 2000 MW system. It is observed that the proposed approach provides a fuel cost saving of up to 1300$ when compared with other referred techniques.

Highly Temperature‐Stable Carbon Nanotube Transistors and Gigahertz Integrated Circuits for Cryogenic Electronics

AbstractCryogenic electronics are attracting more and more attentions owing to the rising of space exploration and quantum computing, in which low‐temperature stable operation is even more concerned than performance of the integrated circuits (ICs). As a promising semiconducting material, carbon nanotube (CNT) has been extensively explored on its low‐temperature transport characteristics, but the cryogenic electronics application of CNT transistors and ICs has seldom been demonstrated. In this work, the low‐temperature operation of field‐effect transistors (FETs) and ICs built on solution‐derived high semiconducting purity randomly oriented CNT film is investigated. The randomly oriented CNT FETs exhibit much higher temperature stability than the individual CNT based FETs and Si transistors from room temperature to liquid nitrogen temperature, and then the ICs constructed by the CNT film FETs present excellent temperature‐stability. Specifically, the fabricated five‐stage ring oscillators (ROs) exhibit oscillation frequency up to 1.5 GHz with the performance change less than 0.5% at the temperature ranging from 300 to 80 K. The work reveals the great potential of high‐performance transistors and ICs built on randomly oriented CNT films in cryogenic electronics applications.

Modeling and Simulation for Performance Evaluation of Optical Quantum Channels in Quantum key Distribution Systems

In this research work, a simulator with time-domain visualizers and configurable parameters using a continuous time simulation approach with Matlab R2019a is presented for modeling and investigating the performance of optical fiber and free-space quantum channels as a part of a generic quantum key distribution system simulator. The modeled optical fiber quantum channel is characterized with a maximum allowable distance of 150 km with 0.2 dB/km at =1550nm. While, at =900nm and =830nm the attenuation values are 2 dB/km and 3 dB/km respectively. The modeled free space quantum channel is characterized at 0.1 dB/km at =860 nm with maximum allowable distance of 150 km also. The simulator was investigated in terms of the execution of the BB84 protocol based on polarizing encoding with consideration of the optical fiber and free-space quantum channel imperfections and losses by estimating the quantum bit error rate and final secure key. This work shows a general repeatable modeling process for significant performance evaluation. The most remarkable result that emerged from the simulated data generated and detected is that the modeling process provides guidance for optical quantum channels design and characterization for other quantum key distribution protocols.

(Invited) Hyperspectral Imaging of MoS2-hBN-Carbon Heteronanotubes: Novel Analytical Method with Optical Resolution of λ/3700

Low-dimensional nanostructures of electronic and/or optical materials possess a large number of new properties due to space quantization, thus exceeding the bulk “parent” materials. Similarly, nanoheterostructures of these materials provide even better control of properties and allow to explore new physics and utilize novel phenomena for device applications. In such systems, the materials properties can vary at the size scale of several nanometers.To meet the challenge of studying nanoheterostructures, the optical materials characterization tools have been recently extended beyond bulk spectroscopy or imaging. A number of Near-Field Optical Microscopy methods were developed. In this online presentation, we will report on a new approach to hyperspectral imaging with scattering Scanning Near-Field Optical Microscopy (sSNOM) which allowed us to perform materials spectroscopy with resolution not restricted by Abbe (diffraction) limit.In 2020, a new class of low-dimensional nanoheterostructure materials – two-dimensional sandwich materials (semiconductor and insulator van der Waals heterostructures) wrapped around carbon nanotube – has been synthesized [1]. Although confirmed by the structural studies (TEM) and elemental analysis (macro- to micro-scale), the heterostructures themselves or their devices were hardly imaged, except for AFM or SEM, not giving materials information. This is due to the diameter of the smallest part ca. 1-2 nm, much beyond the limitations of typical analytical methods.Here we present results on imaging different materials containing the nanoheterostructure with the sSNOM hyperspectral mapping [2]. The maximum resolution (imaging of 2 nm heteronanotube) achieved in these experiments exceeds the inverse wavelength of excitation mid-IR laser ~3,700 times, thus beating diffraction limits of regular optical spectroscopy. Heteronanotubes have been studied on the substrate as well as in real devices (diodes). Imaging of the heteronanotubes through the over-deposited metal electrodes was demonstrated.Acknowledgments: sSNOM work was supported by the National Science Foundation (Grant DMR-2011839). Part of this work was supported by JSPS KAKENHI Grant Numbers JP18H05329, JP20H00220, and by JST, CREST Grant Number JPMJCR20B5, Japan. Part of this work was conducted at Takeda Sentanchi Supercleanroom, supported by “Nanotechnology Platform” of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, Grant number JPMXP09F19UT0006.[1] Xiang, R.; Inoue, T.; Zheng, Y.; Kumamoto, A.; Qian, Y.; Sato, Y.; Liu, M.; Tang, D.; Gokhale, D.; Guo, J.; Hisama, K.; Yotsumoto, S.; Ogamoto, T.; Arai, H.; Kobayashi, Y.; Zhang, H.; Hou, B.; Anisimov, A.; Maruyama, M.; Miyata, Y.; Okada, S.; Chiashi, S.; Li, Y.; Kong, J.; Kauppinen, E. I.; Ikuhara, Y.; Suenaga, K.; Maruyama, S., One-dimensional van der Waals heterostructures. Science 2020, 367 (6477), 537.[2] Y. Feng, H. Li, T. Inoue, S. Chiashi, S. V. Rotkin, R. Xiang, and S. Maruyama, “One-dimensional van der waals hetero-junction diode”, (2020), arXiv:2012.03180.

China’s leading researchers set their sights on new frontiers

China sets lofty goals as it vies for global dominance in the highly competitive fields of quantum science, space exploration and nanocatalysis. China sets lofty goals as it vies for global dominance in the highly competitive fields of quantum science, space exploration and nanocatalysis.

An Introduction to κ-Deformed Symmetries, Phase Spaces and Field Theory

In this review, we give a basic introduction to the κ-deformed relativistic phase space and free quantum fields. After a review of the κ-Poincaré algebra, we illustrate the construction of the κ-deformed phase space of a classical relativistic particle using the tools of Lie bi-algebras and Poisson–Lie groups. We then discuss how to construct a free scalar field theory on the non-commutative κ-Minkowski space associated to the κ-Poincaré and illustrate how the group valued nature of momenta affects the field propagation.

Exceptional Jordan matrix models, octonionic strings/branes and star product deformations

A brief review of the essentials behind the construction of a Chern-Simons-like brane action from the Large N limit of Exceptional Jordan Matrix Models paves the way to the construction of actions for membranes and p-branes moving in octonionic-spacetime backgrounds endowed with octonionic-valued metrics. It is found that the action of a membrane moving in spacetime backgrounds endowed with an octonionic-valued metric is not invariant under the usual diffeomorphisms of its world volume coordinates σa→σ′a(σb), but instead, it is invariant under the rigid E6(−26) transformations which preserve the volume (cubic) form. An extensive study of the bosonic octonionic string moving in flat backgrounds, and its quantization, follows. One of the most significant findings (without invoking supersymmetry) is that the number of degrees of freedom of three (massless) fermion generations is the same as the number of transverse dimensions of an octonionic string moving in D=26 octonionic dimensions. The star-product deformations of octonionic p-branes follow. In particular, we focus on the octonionic membrane along with the phase space quantization methods developed by [30] within the context of Nonassociative Quantum Mechanics. We finalize with an analysis of two octonionic gravitational actions and with some concluding remarks on Double and Exceptional Field theories, Nonassociative Gravity and A∞,L∞ algebras.

Machine learning phase space quantum dynamics approaches.

Derived from phase space expressions of the quantum Liouville theorem, equilibrium continuity dynamics is a category of trajectory-based phase space dynamics methods, which satisfies the two critical fundamental criteria: conservation of the quantum Boltzmann distribution for the thermal equilibrium system and being exact for any thermal correlation functions (even of nonlinear operators) in the classical and harmonic limits. The effective force and effective mass matrix are important elements in the equations of motion of equilibrium continuity dynamics, where only the zeroth term of an exact series expansion of the phase space propagator is involved. We introduce a machine learning approach for fitting these elements in quantum phase space, leading to a much more efficient integration of the equations of motion. Proof-of-concept applications to realistic molecules demonstrate that machine learning phase space dynamics approaches are possible as well as competent in producing reasonably accurate results with a modest computation effort.

Exact analytical treatment of multiqubit noisy dynamics in exchange-coupled semiconductor spin qubits

Charge noise remains the primary obstacle to the development of quantum information technologies with semiconductor spin qubits. We use an exact analytical calculation to determine the effects of quasistatic charge noise on a ring of three equally spaced exchange-coupled quantum dots. We calculate the disorder-averaged return probability from a specific initial state, and use it to determine the coherence time T2* and show that it depends only on the disorder strength and not the mean interaction strength. We also use a perturbative approach to investigate other arrangements of three or four qubits, finding that the return probability contains multiple oscillation frequencies. These oscillations decay in a Gaussian manner, determined by differences in energy levels of the Hamiltonian. We give quantitative values for gate times resulting in several target fidelities. We find that the decoherence time decreases with increasing number of qubits. Our work provides useful analytical insight into the charge noise dynamics of coupled spin qubits.

Nambu dynamics and hydrodynamics of granular material

Abstract On the basis of the intimate relation between Nambu dynamics and hydrodynamics, hydrodynamics on a non-commutative space (obtained by the quantization of space), proposed by Nambu in his last work, is formulated as hydrodynamics of granular material. In Sect. 2, the quantization of space is done using a Moyal product, and the hydrodynamic simulation is performed for the thus-obtained 2D fluid, which flows inside a channel with an obstacle. The obtained results differ between two cases in which the size of a fluid particle is zero and finite. The difference seems to come from the behavior of vortices generated by an obstacle. In Sect. 3, considering a vortex as a string, two models are examined; one is the hybrid model in which vortices interact with each other by exchanging Kalb–Ramond fields (a generalization of stream functions), and the other is the more general string field theory in which the Kalb–Ramond field is one of the excitation modes of string oscillations. In the string field theory, an Altarelli–Parisi-type evolution equation is introduced. This is expected to describe the response of the distribution function of a vortex inside turbulence, when the energy scale is changed. The behavior of viscosity differs in string theory compared with particle theory, so that the Landau theory of fluids to introduce viscosity may be modified. In conclusion, hydrodynamics and string theory are almost identical theories. It should be noted, however, that the string theory needed to reproduce a given hydrodynamics is not the usual string theory.