## Physics

### Chaos in Qubit Coupled Optomechanical Systems. (arXiv:2103.00521v1 [quant-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

We have found stable chaotic solutions for optomechanical systems coupled with a Two-Level System or qubit. In this system methods have been found which can be used to Tune in and out of Chaos as well as various n-period motions. This includes achieving chaos by changing the detuning, coupling parameters, and Power of the driving laser. This allows us to manipulate chaos using either the qubit or the optical cavity. Chaotic motion was also observed in both the qubit and cavity by only changing the relative phase between of driving fields of the two. This gives us the prospect of creating and exploring chaotic motion in quantum mechanical systems with further ease

Categories: Journals, Physics

### A causal and continuous interpretation of the quantum theory: About an original manuscript by David Bohm sent to Louis de Broglie in 1951. (arXiv:2103.00576v1 [physics.hist-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

Categories: Journals, Physics

### Native multiqubit Toffoli gates on ion trap quantum computers. (arXiv:2103.00593v1 [quant-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

We examine the detailed scenario for implementing n-control-qubit Toffoli gates and select gates on ion-trap quantum computers, especially those that shuttle ions into interaction zones. We determine expected performance of these gates with realistic parameters for an ion-trap quantum computer and taking into account the time variation of the exchange integrals. This allows us to estimate the errors due to spin-phonon entanglement as well. While there are challenges with implementing these gates, because their performance always has some degree of error, they should be feasible on current hardware, but they may be too slow to be used efficiently in quantum codes on noisy intermediate scale quantum computers.

Categories: Journals, Physics

### Third quantization of the electromagnetic field. (arXiv:2103.00596v1 [quant-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

We consider an approach in which the usual wave function in the quadrature representation of mode j of the electromagnetic field is quantized to produce a field operator. Since the electromagnetic field is already second quantized, this corresponds to a third quantization. This approach allows certain calculations in quantum optics to be performed in a straightforward way in the Heisenberg picture. Aside from being a useful computational tool, this approach allows an interesting generalization of quantum optics and quantum electrodynamics that could be tested experimentally.

Categories: Journals, Physics

### Non-invertible Anonymous Communication for the Quantum Era. (arXiv:2103.00598v1 [quant-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

We introduce a new approach for circuit anonymous communication based on Lizama's non-invertible Key Exchange Protocol (ni-KEP) which has been conceived to work in the quantum era. Lizama's protocol has the smallest key size when compared to main post-quantum schemes thus it becomes a promising alternative for the quantum era. Circuit-based communication can be scaled to support the Hidden Service Protocol (HSP) as well as cross-domain digital certificates that promise greater computing security, speed and efficiency.

Categories: Journals, Physics

### High-performance parallel classical scheme for simulating shallow quantum circuits. (arXiv:2103.00693v1 [quant-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

Recently, constant-depth quantum circuits are proved more powerful than their classical counterparts at solving certain problems, e.g., the two-dimensional (2D) hidden linear function (HLF) problem regarding a symmetric binary matrix. To further investigate the boundary between classical and quantum computing models, in this work we propose a high-performance two-stage classical scheme to solve a full-sampling variant of the 2D HLF problem, which combines traditional classical parallel algorithms and a gate-based classical circuit model together for exactly simulating the target shallow quantum circuits. Under reasonable parameter assumptions, a theoretical analysis reveals our classical simulator consumes less runtime than that of near-term quantum processors for most problem instances. Furthermore, we demonstrate the typical all-connected 2D grid instances by moderate FPGA circuits, and show our designed parallel scheme is a practically scalable, high-efficient and operationally convenient tool for simulating and verifying graph-state circuits performed by current quantum hardware.

Categories: Journals, Physics

### Disorder Enhanced Quantum Process Tomography using Quantum Light. (arXiv:2103.00696v1 [physics.chem-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

Quantum process tomography might be the most important paradigm shift which has yet to be translated fully into theoretical chemistry. Its fundamental strength, long established in quantum information science, offers a wealth of information about quantum dynamic processes which lie at the heart of many (if not all) chemical processes. However, due to its complexity its application to real chemical systems is currently beyond experimental reach. Furthermore, it is susceptible to errors due to experimental and theoretical inaccuracies and disorder has long been thought to be an obstacle in its applicability. Here, I present the first results of a study into the use of quantum light for quantum process tomography. By using a toy model and comparing numerical simulations to theoretical predictions the possible enhancement of using non-conventional light is studied. It is found, however, that disorder is necessary make the use of quantum light suitable for process tomography and that, in contrast to conventional wisdom, disorder can make the results more accurate than in an ordered system.

Categories: Journals, Physics

### Nonlinear dynamics and quantum chaos of a family of kicked $p$-spin models. (arXiv:2103.00748v1 [quant-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

We introduce kicked $p$-spin models describing a family of transverse Ising-like models for an ensemble of spin-$1/2$ particles with all-to-all $p$-body interaction terms occurring periodically in time as delta-kicks. This is the natural generalization of the well-studied quantum kicked top ($p$=2). We fully characterize the classical nonlinear dynamics of these models, including the transition to global Hamiltonian chaos. The classical analysis allows us to build a classification for this family of models, distinguishing between $p=2$ and $p>2$, and between models with odd and even $p$'s. Quantum chaos in these models is characterized in both kinematic and dynamic signatures. For the latter we show numerically that the growth rate of the out-of-time-order correlator is dictated by the classical Lyapunov exponent. Finally, we argue that the classification of these models constructed in the classical system applies to the quantum system as well.

Categories: Journals, Physics

### Magnetic-Torque Enhanced by Tunable Dipolar interactions. (arXiv:2103.00836v1 [cond-mat.mes-hall])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

We use tunable dipolar-interactions between the spins of nitrogen-vacancy (NV) centers in diamond to rotate a diamond crystal. Specifically, we employ cross-relaxation between the electronic spin of pairs of NV centers in a trapped diamond to enhance the anisotropic NV paramagnetism and thus to increase the associated spin torque. Our observations open a path towards the use of mechanical oscillators to detect paramagnetic defects that lack optical transitions, to investigation of angular momentum conservation in spin relaxation processes and to novel means of cooling the motion of mechanical oscillators.

Categories: Journals, Physics

### Improved non-linear devices for quantum applications. (arXiv:2103.00873v1 [quant-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

In this paper, we review the state of the art of mode selective, integrated sum-frequency generation devices tailored for quantum optical technologies. We explore benchmarks to asses their performance and discuss the current limitations of these devices, outlining possible strategies to overcome them. Finally, we present the fabrication of a new, improved device and its characterization. We analyse the fabrication quality of this device and discuss the next steps towards improved non-linear devices for quantum applications.

Categories: Journals, Physics

### Pulsed characteristic-function measurement of a damped harmonic oscillator. (arXiv:2103.00877v1 [quant-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

We present a method for the direct measurement of the Wigner characteristic function of a damped harmonic oscillator that is completely inaccessible for control or measurement. The strategy employs a recently proposed probe-measurement-based scheme [Phys. Rev. Lett. 122, 110406 (2019)] which relies on the pulsed control of a two-level probe. We generalize this scheme to the case of a non-unitary time evolution of the target harmonic oscillator, describing its damping by a finite-temperature environment, given in the form of a Lindblad master equation. This generalization is achieved using a superoperator formalism and yields analytical expressions for the direct measurement of the characteristic function, accounting for the decoherence during the measurement process.

Categories: Journals, Physics

### Monogamy of quantum discord. (arXiv:2103.00924v1 [quant-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

We explore all the trade-off relations of multipartite quantum discord proposed very recently in [Phys. Rev. Lett. {124}, 110401~(2020)] and show that the multipartite quantum discord is completely monogamous provided that it does not increase under discard of subsystems. Here, a quantity of multipartite quantity, with the same spirit as established in [Phys. Rev. A. {101}, 032301~(2020)], is said to be completely monogamous (i) if it does not increase under loss of subsystems and (ii) if some given combination of subsystems reach the total amout of correlation, then all other combination of subsystems that excluding the given subsystems do not contain such a correlation any more. In addition, we explore all the trade-off relations for the global quantum discord proposed in [Phys. Rev. A 84, 042109 (2011)] and show that the global quantum discord is not completely monogamous.

Categories: Journals, Physics

### Information geometry for Fermi-Dirac and Bose-Einstein quantum statistics. (arXiv:2103.00935v1 [quant-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

Information geometry is an emergent branch of probability theory that consists of assigning a Riemannian differential geometry structure to the space of probability distributions. We present an information geometric investigation of gases following the Fermi-Dirac and the Bose-Einstein quantum statistics. For each quantum gas, we study the information geometry of the curved statistical manifolds associated with the grand canonical ensemble. The Fisher-Rao information metric and the scalar curvature are computed for both fermionic and bosonic models of non-interacting particles. In particular, by taking into account the ground state of the ideal bosonic gas in our information geometric analysis, we find that the singular behavior of the scalar curvature in the condensation region disappears. This is a counterexample to a long held conjecture that curvature always diverges in phase transitions.

Categories: Journals, Physics

### Single-beam all-optical non-zero field magnetometric sensor for magnetoencephalography applications. (arXiv:2103.00967v1 [physics.optics])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

We present a method for measuring the magnetic field that allows hyperfine and Zeeman optical pumping, excitation and detection of magnetic resonance by means of one laser beam with ellipticity modulated in time. This improvement allows us to significantly simplify the Bell-Bloom magnetometric scheme, while retaining all its metrological and technical advantages The method does not require the use of radio frequency fields, which is essential when creating arrays of sensors. The results of experimental studies demonstrate the efficiency of the proposed method and its potential applicability in most challenging magnetoencephalographic tasks.

Categories: Journals, Physics

### Evolution of projective measurements under qubit channels and associated energy cost. (arXiv:2103.00974v1 [quant-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

The action of qubit channels on projective measurements on a qubit state is used to establish an equivalence between channels and properties of generalized measurements characterized by bias and sharpness parameters. This can be interpreted as shifting the description of measurement dynamics from the Schrodinger to the Heisenberg picture. In particular, unital (non-unital) quantum channels are shown to induce unbiased (biased) measurements. The Markovian channels are found to be equivalent to measurements for which sharpness is a monotonically decreasing function of time. These results are illustrated by considering various noise channels. Further, the effect of bias and sharpness parameters on the energy cost of a measurement and its interplay with the non-Markovian dynamics is also discussed.

Categories: Journals, Physics

### Resolution of the spin paradox in the Nilsson model. (arXiv:2103.00979v1 [nucl-th])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

In the well-known Nilsson diagrams, depicting the dependence of the nuclear single-particle energy levels on quadrupole deformation, a spin paradox appears {as the deformation sets in, leading from spherical shapes to prolate deformed shapes with cylindrical symmetry}. Bunches of levels corresponding to a spherical shell model orbital, sharing the same orbital angular momentum and the same total angular momentum, appear to correspond to Nilsson energy levels, labeled by asymptotic quantum numbers in cylindrical coordinates, some of which have spin up, while some others have spin down. Furthermore, for some orbitals the correspondence between spherical shell model quantum numbers and Nilsson asymptotic quantum numbers is not the same for protons and for neutrons. Introducing a new rule of correspondence between the two sets of quantum numbers, we show that the spin paradox is resolved and full agreement between the proton and neutron Nilsson diagrams is established. The form of the Nilsson diagrams as a function of the quadrupole deformation remains unchanged, the only difference between the new diagrams and the traditional ones being the mutual exchange of the Nilsson labels for certain pairs of single-particle energy levels.

Categories: Journals, Physics

### Relativistic corrections to the Di{\'o}si-Penrose model. (arXiv:2103.00994v1 [quant-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

The Di{\'o}si-Penrose model is explored in a relativistic context. Relativistic effects were considered within a recently proposed Grave de Peralta approach [L. Grave de Peralta, {\em Results Phys.} {\bf 18} (2020) 103318], which parametrize the Schr{\"o}dinger-like hamiltonian so as to impose that the average kinetic energy of the system coincide with its relativistic kinetic energy. As a case of study, the method is applied to a particle in a box with good results. In the Di{\'o}si-Penrose model we observed that the width of a quantum matter field confined by its own gravitational field [L. Di{\'o}si, {\em Phys. Lett}. {\bf 105A} (1984) 199], sharply drop to zero for a mass of the order of the Planck mass, indicating a breakdown of the model at the Planck scale.

Categories: Journals, Physics

### Duality Symmetry of Quantum Electrodynamics. (arXiv:2103.01000v1 [quant-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

The duality symmetry between electricity and magnetism hidden in classical Maxwell equations suggests the existence of dual charges, which have usually been interpreted as magnetic charges and have never been observed in experiments. In quantum electrodynamics (QED), both the electric and magnetic fields have been unified into one gauge field $A_{\mu}$, which makes this symmetry inconspicuous. Here, we recheck the duality symmetry of QED by introducing a dual gauge field. Within the framework of gauge-field theory, we first show that the electric-magnetic duality symmetry cannot give any new conservation law. By checking charge-charge interaction and specifically the quantum Lorentz force equation, we find that the dual charges are electric charges, not magnetic charges. More importantly, we show that true magnetic charges are not compatible to the gauge-field theory of QED, because the interaction between a magnetic charge and an electric charge can not be mediated by gauge photons.

Categories: Journals, Physics

### Direct measurement of ultrafast temporal wavefunctions. (arXiv:2103.01020v1 [quant-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

The large capacity and robustness of information encoding in the temporal mode of photons is important in quantum information processing, in which characterizing temporal quantum states with high usability and time resolution is essential. We propose and demonstrate a direct measurement method of temporal complex wavefunctions for weak light at a single-photon level with subpicosecond time resolution. Our direct measurement is realized by ultrafast metrology of the interference between the light under test and self-generated monochromatic reference light; no external reference light or complicated post-processing algorithms are required. Hence, this method is versatile and potentially widely applicable for temporal state characterization.

Categories: Journals, Physics

### Scattering Problems via Real-time Wave Packet Scattering. (arXiv:2103.01027v1 [physics.ed-ph])

arXiv.org: Quantum Physics - Tue, 2021-03-02 10:25

In this paper, we use a straightforward numerical method to solve scattering models in one-dimensional lattices based on a tight-binding band structure. We do this by using the wave packet approach to scattering, which presents a more intuitive physical picture than the traditional plane wave approach. Moreover, a general matrix diagonalization method that is easily accessible to undergraduate students taking a first course in quantum mechanics is used. Beginning with a brief review of wave packet transport in the continuum limit, comparisons are made with its counterpart in a lattice. The numerical results obtained through the diagonalization method are then benchmarked against analytic results. The case of a resonant dimer is investigated in the lattice, and several resonant values of the mean wave packet momentum are identified. The transmission coefficients obtained for a plane wave incident on a step potential and rectangular barrier are compared by investigating an equivalent scenario in a lattice. Lastly, we present several short simulations of the scattering process which emphasize how a simple methodology can be used to visualize some remarkable phenomena.

Categories: Journals, Physics