Superposition Of States Research Articles

Statistical Properties of Superpositions of Coherent Phase States with Opposite Arguments

We calculate the second-order moments, the Robertson–Schrödinger uncertainty product, and the Mandel factor for various superpositions of coherent phase states with opposite arguments, comparing the results with similar superpositions of the usual (Klauder–Glauber–Sudarshan) coherent states. We discover that the coordinate variance in the analog of even coherent states can show the most strong squeezing effect, close to the maximal possible squeezing for the given mean photon number. On the other hand, the Robertson–Schrödinger (RS) uncertainty product in superpositions of coherent phase states increases much slower (as function of the mean photon number) than in superpositions of the usual coherent states. A nontrivial behavior of the Mandel factor for small mean photon numbers is discovered in superpositions with unequal weights of two components. An exceptional nature of the even and odd superpositions is demonstrated.

CNOT Quantum Gate Based on Spatial Photonic Qubits Under Resonant Electro-Optical Control

A theoretical model of a quantum node that implements the two-qubit CNOT operation with use of photonic qubits with spatial encoding is considered. Each qubit is represented by a pair of modes supporting an arbitrary superposition of single-photon states. The active element of the node is a single or double quantum dot with a tunable frequency, which coherently exchanges an energy quantum with the modes. The spectral characteristics of the quantum node elements are simulated. The probability of implementation of a controlled inversion of the qubit state is calculated depending on the system parameters.

Pseudoentropy sum rule by analytical continuation of the superposition parameter

Abstract In this paper, we establish a sum rule that connects the pseudoentropy and entanglement entropy of the superposition state. Through analytical continuation of the superposition parameter, we demonstrate that the transition matrix and density matrix of the superposition state can be treated in a unified manner. Within this framework, we naturally derive sum rules for the (reduced) transition matrix, pseudo-Rényi entropy, and pseudoentropy. Furthermore, we demonstrate the close relationship between the sum rule for pseudoentropy and the singularity structure of the entropy function for the superposition state after analytical continuation. We also explore potential applications of the sum rule, including its relevance to understanding the gravity dual of non-Hermitian transition matrices and establishing upper bounds for the absolute value of pseudoentropy.

Fast and robust production of quantum superposition states by the fractional shortcut to adiabaticity

The fractional shortcut to adiabaticity (f-STA) for the production of quantum superposition states is proposed firstly via a three-level system with a Λ-type linkage pattern and a four-level system with a tripod structure. The fast and robust production of the coherent superposition states is studied by comparing the populations for the f-STA and the fractional stimulated Raman adiabatic passage (f-STIRAP). The states with equal proportions can be produced by fixing the controllable parameters of the driving pulses at the final moment of the whole process. The effects of the pulse intensity and the time delay of the pulses on the production process are discussed by monitoring the populations on all of the quantum states. In particular, the spontaneous emission arising from the intermediate state is investigated by the quantum master equation. The result reveals that the f-STA exhibits superior advantages over the f-STIRAP in producing the superposition states.

High-dimensional spin-orbital single-photon sources.

Hybrid integration of solid-state quantum emitters (QEs) into nanophotonic structures opens enticing perspectives for exploiting multiple degrees of freedom of single-photon sources for on-chip quantum photonic applications. However, the state-of-the-art single-photon sources are mostly limited to two-level states or scalar vortex beams. Direct generation of high-dimensional structured single photons remains challenging, being still in its infancy. Here, we propose a general strategy to design highly entangled high-dimensional spin-orbital single-photon sources by taking full advantage of the spatial freedom to design QE-coupled composite (i.e., Moiré/multipart) metasurfaces. We demonstrate the generation of arbitrary vectorial spin-orbital photon emission in high-dimensional Hilbert spaces, mapping the generated states on hybrid-order Bloch spheres. We further realize single-photon sources of high-dimensional spin-orbital quantum emission and experimentally verify the entanglement of high-dimensional superposition states with high fidelity. We believe that the results obtained facilitate further progress in integrated solutions for the deployment of next-generation high-capacity quantum information technologies.

Quantum decoherence effects: A complete treatment

Physical systems in real life are inextricably linked to their surroundings and never completely separated from them. Truly closed systems do not exist. The phenomenon of decoherence, which is brought about by the interaction with the environment, removes the relative phase of quantum states in superposition and makes them incoherent. In neutrino physics, decoherence, although extensively studied has only been analyzed thus far exclusively in terms of its dissipative characteristics. While it is true that dissipation, or the exponential suppression, eventually is the main observable effect, the exchange of energy between the medium and the system, is an important factor that has been overlooked up until now. In this work, we introduce this term and analyze its consequences. Published by the American Physical Society 2024

Coded communication study of Laguerre–Gaussian vortex beam and its superposition states in underwater turbulence

Using theoretical and experimental approaches, we have investigated coded communications for the Laguerre–Gaussian (LG) beam and its superposition states in an oceanic turbulent environment. We established an ocean turbulence transmission model and constructed an underwater vortex beam-coded communication experiment, generating light-intensity images of the LG beam and its superposition states transmitted in different simulated ocean turbulence environments. These simulated and experimentally obtained light-intensity images were grayed out, detected and identified, symbol coded, and decoded by the Visual Geometry Group neural network to study the bit error rate (BER) of the LG beam and its superposition states for coded communication in the simulated ocean turbulence environment. The study results show that the BER increases with increasing transmission distance and simulated ocean turbulence intensity. This study provides an important reference for the further development of optical communication and network technology in high-speed data transmission and communication capability enhancement.

On gravity implication in the wavefunction collapse

Abstract Inspired by an ontic view of the wavefunction in quantum mechanics and motivated
by the universal e¤ect of gravity, we discuss a possible gravity implication in the reduc-
tion scenario of the quantum state. Concretely, we investigate the stability of the spatial
superposition of a massive quantum state under the gravity e¤ect. In this context, we
argue that the stability of the spatially superposed state jYi =
nå
i=1
ai jyii, ai 2 C, depends
on its gravitational self-energy UG
Y originating from the effective mass density distribution
r m (x) through the spatially localized eigenstates jyii. We reveal that the gravitational
self-interaction between the di¤erent spacetime curvatures jGii created by the eigenstate
e¤ective masses m y leads to the reduction of the superposed state to one of the possible
localized states jyki jGki. Among others, we discuss such a gravity-driven state reduc-
tion. Then, we approach the corresponding collapse time t Collapse Y and the induced effective electric current I Y in the case of a charged state, as well as the possible detection aspects.

Quantum entanglement to extract a true ground state from an approximate ground state

Abstract We propose a procedure to extract a true ground state from an approximate ground state by using quantum entanglement. We use plural ancilla qubits with hierarchical structure, intending to gradually put up approximate precision. We demonstrate the procedure for quantum systems with a few qubits that derive from the (1+1)-dimensional Schwinger model by classically emulated digital quantum simulation. Although we use for simplicity an approximate ground state prepared by the adiabatic quantum computation, our procedure is applicable any approximate ground state that is a superposition of a true ground state and excited states. Our procedure is applicable for an N-qubits Hamiltonian with a non-degenerate ground state.

Transmission characteristics of vortex light superposition in atmospheric turbulence disturbed by plane acoustic waves

Herein, we derive the expression for the atmospheric refractive index structure constant under the influence of planar acoustic wave perturbations under the influence of the acoustic field on the refractive index and energy of the atmosphere. Utilizing the low-frequency compensated power spectrum inversion technique, we simulate the refractive index power spectrum of atmospheric turbulence perturbed by a planar acoustic wave. Numerical analysis is conducted on the transmission characteristics of the vortex light superposition states in atmospheric turbulence perturbed by a plane acoustic wave under different acoustic wave transmission heights, acoustic pressure amplitudes, and frequencies. Results indicate that introducing an acoustic field induces fluctuations in the atmospheric refractive index structure constant, with a more pronounced impact on the refractive index than on energy. Compared with the sole consideration of the impact of the acoustic field on the atmospheric refractive index, incorporating its effect on atmospheric energy results in a decrease in the atmospheric refractive index structure constant. The impact of the acoustic field on atmospheric turbulence is directly proportional to both acoustic pressure amplitude and frequency. The influence of the acoustic field on the transmission properties of the vortex optical superposition state varies with different acoustic transmission distances. Consequently, the transmission characteristics of the vortex light superposition state can be actively modulated according to varying acoustic wave transmission distances. This study offers a theoretical basis for modulating the optical field transmission characteristics via acoustic fields.

The quantum mechanical origin of the supercapacitance phenomenon in reduced graphene oxide structures

We investigated supercapacitance phenomena observed in reduced graphene oxide structures from a quantum mechanical rate viewpoint. The supercapacitance phenomenon in carbonaceous materials has been majorly attributed to electrostatic capacitance contributions, in which the magnitude of this capacitance is correlated with the amount of surface area available to be charged under the presence of electric potential perturbations. Nonetheless, the quantum rate theory predicts a superposition between electrostatic Ce and chemical Cq (also called quantum) capacitance energetic levels. The superposition of these capacitive states implies that the electric potential perturbation not only drives the separation of charges in space (thus correlating with the geometry of the capacitor and consequently with the surface area) but also governs the occupancy of the electric-field screened electronic structure of reduced graphene oxide embedded in the electrolyte environment. This leads to an energy degeneracy between electrostatic e2/Cq and quantum e2/Cq capacitive energy states, as confirmed in this work for reduced graphene oxide carbonaceous structures. Accordingly, the analysis proves that the charge dynamics associated with the resistance for charging the pseudo-capacitive E=e2/Cq states of reduced graphene oxide structure follows a quantum resistance limit RK=h/e2∼25.8 kΩ within a charging frequency of ν=1/RKCq=E/h=e2/hCq that obeys quantum electrodynamics principles, in agreement with the premises of the quantum rate theory. Two energy levels associated with the occupancy of the electronic states upon the reduction of graphene oxide were identified.

On the effectiveness of the collapse in the Diósi–Penrose model

Abstract The possibility that gravity plays a role in the collapse of the quantum wave function has been considered in the literature, and it is of relevance not only because it would provide a solution to the measurement problem in quantum theory, but also because it would give a new and unexpected twist to the search for a unified theory of quantum and gravitational phenomena, possibly overcoming the current impasse. The Diósi–Penrose model is the most popular incarnation of this idea. It predicts a progressive breakdown of quantum superpositions when the mass of the system increases; as such, it is susceptible to experimental verification. Current experiments set a lower bound R 0 ≳ 4 Å for the free parameter of the model, excluding some versions of it. In this work we search for an upper bound, coming from the request that the collapse is effective enough to guarantee classicality at the macroscopic scale: we find out that not all macroscopic systems collapse effectively. If one relaxes this request, a reasonable (although to some degree arbitrary) bound is found to be: R 0 ≲ 10 6 Å. This will serve to better direct future experiments to further test the model.

Survey Paper on Quantum Deep Reinforcement Learning for Robot Navigation Tasks

Abstract: Quantum deep reinforcement learning is an integration of the principles of quantum computing with deep reinforcement learning in an effort to advance robot navigation tasks. Due to the explosion of the state and action spaces, traditionally DRL methods are limited in scalability and efficiency. QDRL, however, uses quantum superposition and entanglement for more efficient processing of big amounts of information-it enables robots to learn optimal policies for navigating complex environments. We introduce here a new QDRL framework in which quantum neural networks encode policy functions and value estimates. We demonstrate how quantum circuits can take advantage of multi-dimensional state representations in order to strengthen the power of a robot in changing its environment over time. Benchmark experiments on navigation tasks reflect phenomenal acceleration in learning performance along with better decision-making accuracy compared to classical DRL methods. We then consider integrating such quantum algorithms, as Grover's search, to improve exploration strategies in sparse reward settings. The experiments show that QDRL speeds up convergence rates and provides robots with the possibility to react more rapidly to unexpected obstacles. It discusses new applications for quantum computing of autonomous systems, potentially applied to robotics, autonomous vehicles, and other environments which require complex decision making. Some lines of work in the future are optimization of the resources needed for quantum computers and hybrid architectures for the resolution of classical problems in navigation

DNA Gene’s Basic Structure as a Nonperturbative Circuit Quantum Electrodynamics: Is RNA Polymerase II the Quantum Bus of Transcription?

Previously, we described that Adenine, Thymine, Cytosine, and Guanine nucleobases were superconductors in a quantum superposition of phases on each side of the central hydrogen bond acting as a Josephson Junction. Genomic DNA has two strands wrapped helically around one another, but during transcription, they are separated by the RNA polymerase II to form a molecular condensate called the transcription bubble. Successive steps involve the bubble translocation along the gene body. This work aims to modulate DNA as a combination of n-nonperturbative circuits quantum electrodynamics with nine Radio-Frequency Superconducting Quantum Interference Devices (SQUIDs) inside. A bus can be coupled capacitively to a single-mode microwave resonator. The cavity mode and the bus can mediate long-range, fast interaction between neighboring and distant DNA SQUID qubits. RNA polymerase II produces decoherence during transcription. This enzyme is a multifunctional biomolecular machine working like an artificially engineered device. Phosphorylation catalyzed by protein kinases constitutes the driving force. The coupling between n-phosphorylation pulses and any particular SQUID qubit can be obtained selectively via frequency matching.

Decoherence of spin superposition state caused by a quantum electromagnetic field

Decoherence of spin superposition state caused by a quantum electromagnetic field

Universal limit on spatial quantum superpositions with massive objects due to phonons

It has been a long-standing goal to bring massive objects into a superposition of different locations in real space, not only to confirm quantum theory in new regimes, but also to explore the interface with gravity. The main challenge is usually thought to arise from forces or scattering due to environmental fields and particles that decohere the large object's wave function into a statistical mixture. We unveil a decoherence channel which cannot be eliminated by improved isolation from the environment. It originates from sound waves within the object, which are excited as part of any splitting process and carry partial information. This puts stringent constraints on future spatial superpositions of large objects. Published by the American Physical Society 2024

Spin-bearing molecules as optically addressable platforms for quantum technologies

Abstract Efforts to harness quantum hardware relying on quantum mechanical principles have been steadily progressing. The search for novel material platforms that could spur the progress by providing new functionalities for solving the outstanding technological problems is however still active. Any physical property presenting two distinct energy states that can be found in a long-lived superposition state can serve as a quantum bit (qubit), the basic information processing unit in quantum technologies. Molecular systems that can feature electron and/or nuclear spin states together with optical transitions are one of the material platforms that can serve as optically addressable qubits. The attractiveness of molecular systems for quantum technologies relies on the fact that molecular structures of atomically defined nature can be obtained in endless diversity of chemical compositions. Crucially, by harnessing the molecular design protocols, the optical and spin (electronic and nuclear) properties of molecules can be tailored, aiding the design of optically addressable spin qubits and quantum sensors. In this contribution, we present a concise and collective discussion of optically addressable spin-bearing molecules – namely, organic molecules, transition metal (TM) and rare-earth ion (REI) complexes – and highlight recent results such as chemical tuning of optical and electron spin quantum coherence, optical spin initialization and readout, intramolecular quantum teleportation, optical coherent storage, and photonic-enhanced optical addressing. We envision that optically addressable spin-carrying molecules could become a scalable building block of quantum hardware for applications in the fields of quantum sensing, quantum communication and quantum computing.

Quantum networks theory

The formalism of quantum theory over discrete systems is extended in two significant ways. First, quantum evolutions are generalized to act over entire network configurations, so that nodes may find themselves in a quantum superposition of being connected or not, and be allowed to merge, split and reconnect coherently in a superposition. Second, tensors and traceouts are generalized, so that systems can be partitioned according to almost arbitrary logical predicates in a robust manner. The hereby presented mathematical framework is anchored on solid grounds through numerous lemmas. Indeed, one might have feared that the familiar interrelations between the notions of unitarity, complete positivity, trace-preservation, non-signalling causality, locality and localizability that are standard in quantum theory be jeopardized as the neighbourhood and partitioning between systems become both quantum, dynamical, and logical. Such interrelations in fact carry through, albeit two new notions become instrumental: consistency and comprehension.

Generation of ultrarelativistic vortex leptons with large orbital angular momenta

We put forward a novel method for generating ultrarelativistic vortex positrons and electrons with intrinsic orbital angular momenta (OAM) through nonlinear Breit-Wheeler (NBW) scattering of vortex γ photons. A complete angular momentum-resolved scattering theory has been formulated, introducing angular momenta of laser photons and vortex particles into the conventional NBW scattering framework. We find that vortex positron (electron) can be produced when the outgoing electron (positron) is generated along the collision axis. By unveiling the angular momentum transfer mechanism, we clarify that the OAM of the γ photon and the large angular momenta due to multiple laser photons are entirely transferred to the generated vortex leptons. Furthermore, the cone opening angle and superposition state of the vortex γ photon can be determined via the angular distribution of created pairs in NBW processes. Published by the American Physical Society 2024

Teaching quantum mechanics using Ant–Man

Abstract The integration of popular culture, particularly superhero films, into physics education has gained traction as a means to enhance student engagement and comprehension. In this paper, we present a pedagogical approach aimed at introducing quantum mechanics concepts to high school students using the superhero paradigm, focusing on Ant–Man. Our approach addresses the lack of resources utilizing quantum physics in superhero films by outlining a sequence of activities centred around the Uncertainty Principle, position, momentum, superposition of states, and the Planck scale. Through a series of classroom activities, students were encouraged to reflect on quantum mechanical concepts, propose solutions to fictional scenarios inspired by superhero narratives, and apply their understanding to new problem–solving situations. Analysis of student responses indicates that the activities effectively stimulated introductory discussions and curiosity about quantum mechanics, suggesting potential for further exploration and adaptation in physics education.