Abstract
Quantum microwave transmission is key to realizing modular superconducting quantum computers and distributed quantum networks. A large number of incoherent photons are thermally generated ...within the microwave frequency spectrum. The closeness of the transmitted quantum state to the source-generated quantum state at the input of the transmission link (measured by the transmission fidelity) degrades due to the presence of the incoherent photons. Hence, high-fidelity quantum microwave transmission has long been considered to be infeasible without refrigeration. In this study, we propose a novel method for high-fidelity quantum microwave transmission using a room-temperature lossy waveguide. The proposed scheme consists of connecting two cryogenic nodes (i.e., a transmitter and a receiver) by the room-temperature lossy microwave waveguide. First, cryogenic preamplification is implemented prior to transmission. Second, at the receiver side, a cryogenic loop antenna is placed inside the output port of the waveguide and coupled to an
LC
harmonic oscillator located outside the waveguide. The loop antenna converts quantum microwave fields to a quantum voltage across the coupled
LC
harmonic oscillator. Noise photons are induced across the
LC
oscillator including the source generated noise, the preamplification noise, the thermal occupation of the waveguide, and the fluctuation-dissipation noise. The loop antenna detector at the receiver is designed to extensively suppress the induced photons across the
LC
oscillator. The signal transmittance is maintained intact by providing significant preamplification gain. Our calculations show that high-fidelity quantum transmission (i.e., more than
$$95\%$$
95
%
) is realized based on the proposed scheme for transmission distances reaching 100 m.
We evaluate the localization length of the wave solution of a random potential characterized by an arbitrary autocorrelation function. We go beyond the Born approximation to evaluate the localization ...length using a non-linear approximation and calculate all the correlators needed for the localization length expression. We compare our results with numerical results for the special case, where the autocorrelation decays quadratically with distance. We look at disorder ranging from weak to strong disorder, which shows excellent agreement. For the numerical simulation, we introduce a generic method to obtain a random potential with an arbitrary autocorrelation function. The correlated potential is obtained in terms of the convolution between a Wiener stochastic potential and a function of the correlation.
Graphical abstract
We explore the phase space quantum effects, quantum coherence and non-classicality, for two coupled identical qubits with intrinsic decoherence. The two qubits are in a nonlinear interaction with a ...quantum field via an intensity-dependent coupling. We investigate the non-classicality via the Wigner functions. We also study the phase space information and the quantum coherence via the Q-function, Wehrl density, and Wehrl entropy. It is found that the robustness of the non-classicality for the superposition of coherent states, is highly sensitive to the coupling constants. The phase space quantum information and the matter-light quantum coherence can be controlled by the two-qubit coupling, initial cavity-field and the intrinsic decoherence.
The quest for quantum advantage, wherein quantum computers surpass the computational capabilities of classical computers executing state-of-the-art algorithms on well-defined tasks, represents a ...pivotal race in the domain of quantum computing. NISQ (Noisy Intermediate-Scale Quantum) computing has witnessed remarkable advancements, culminating in significant milestones on the journey towards the realization of universal fault-tolerant quantum computers. This transformative turning point, known as quantum supremacy, has been achieved amid a series of breakthroughs, signifying the dawn of the quantum era. Quantum hardware has undergone substantial integration and architectural evolution, contrasting with its nascent stages. In this review, we critically examine the quantum supremacy experiments conducted thus far, shedding light on their implications and contributions to the evolving landscape of quantum computing. Additionally, we endeavor to illuminate a range of cutting-edge proof-of-principle investigations in the realm of applied quantum computing, providing an insightful overview of the current state of applied quantum research and its prospective influence across diverse scientific, industrial, and technological frontiers.
Abstract
We investigate the evolution of coupled optical solitons in a multilayer graphene medium. The considered graphene medium is subjected to microwave voltage biasing. The coupled two optical ...solitons emerge through the electrical (i.e., microwave voltage) perturbation of the effective permittivity of the graphene multilayer. We show that the coupled solitons are electrically adjustable by controlling the amplitude and frequency of the biasing microwave voltage. Importantly, this proposed regime of electrically controlled optical solitons offers a modality to generate entangled optical solitons and two-mode squeezed solitons. Furthermore, the hybrid interaction that includes both the driving microwave voltage and the optical solitons yields a platform to combine the two worlds of quantum photonics and quantum superconducting systems.
Noisy intermediate-scale quantum computers (NISQ) have demonstrated superior performance compared to conventional computing schemes. Nonetheless, errors associated with two-qubit entangling gates ...remain a substantial obstacle in fully harnessing the potential of current superconducting quantum computers. The achievement of quantum computation and quantum information processing critically depends on the presence of entangled states. These states are indispensable for quantum computers to surpass classical computers in terms of computational power. This paper presents a comprehensive characterization of a two-qubit entangling gate, known as Dagwood Bumstead (DB) gate, to investigate the challenges posed by errors in the DB gate on NISQ devices. Firstly, we propose a scheme for the realization of the DB gate using two capacitively coupled Josephson Superconducting qubits, based on the experimental setup carried out in Bialczak et al. (2010). Additionally, we introduce and characterize a novel two-qubit quantum gate. Our proposed gate showcases an impressive average gate fidelity of 0.85450. The DB gate’s performance is fully described through quantum process tomography (QPT) and quantum state tomography (QST) experiments conducted in three different environments: noisy, noiseless, and on a real IBM quantum computer. The process fidelity of the DB gate is measured to be 0.8069705, and the state fidelity is determined to be 0.8858750. This study offers valuable insights into the performance of the DB gate on a NISQ device, showcasing its potential for executing intricate algorithms and operations on an authentic quantum computer.
We propose a novel approach for microwave and optical fields entanglement using an electrical capacitor loaded with graphene plasmonic waveguide. In the proposed scheme, a quantum microwave signal of ...frequency {\omega_{m}} drives the electrical capacitor, while an intensive optical field (optical pump) of frequency {\omega_{1}} is launched to the graphene waveguide as a surface plasmon polariton (i.e., SPP) mode. The two fields interact by the means of electrically modulating the graphene optical conductivity. It then follows that an upper and lower SPP sideband modes (of {\omega_{2}=\omega_{1}+\omega_{m}} and {\omega_{3}=\omega_{1}-\omega_{m}} frequencies, respectively) are generated. We show that the microwave signal and the lower sideband SPP mode are entangled, for a proper optical intensity. A quantum mechanics model is carried out to describe the fields evolution. Furthermore, novel iterative approach (based on combining the Duan criterion with the quantum regression theorem) is developed to assess the fields entanglement. Consequently, the entanglement of the two fields is evaluated versus several parameters including the waveguide length, the pump intensity, and the microwave frequency. We find that the two fields are entangled over a vast microwave frequency range. Moreover, our calculations show that a significant number of entangled photons are generated at the lower SPP sideband. The proposed scheme attains tunable mechanism for microwave-optical entanglement which paves the way for efficient quantum systems.
A graphene-based layered structure is proposed for tunable conversion of quantum microwave signal to the optical frequency domain. The structure is composed of graphene layers filled with dielectric ...materials of different permittivities. The quantum microwave signal is driving the graphene layers. An optical pump signal is launched to the graphene layers. It then follows that an optical modulation is conducted, through electrically modifying the graphene conductivity, which results in generating an upper and lower optical sidebands. The destruction resonance of the layered medium is used to suppress the lower optical sideband; achieving low noise conversion. A quantum mechanics analysis is developed to model the interacting fields. In this work, two different filling materials are considered to enhance the destruction resonance of the grahene layers. Hence, significant suppression of the lower sideband is achieved. The presented numerical simulations show that large number (several hundreds) of converted photons can be achieved with only few tens of graphene layers, while efficient lower sideband suppression is attained. Importantly, the converted microwave frequency can be tuned over a vast range by altering the frequency of the optical pump.
Quantum teleportation draws our attention to propose a new type of problems which can not be solved using classical computers. In this paper, we propose one of these problems. Concretely, this paper ...extends the definition of Deutsch’s problem to decide whether a black box Uf applied on a given unknown qubit α|0〉+β|1〉, such that |α|>0,|β|>0,and|α|≠|β|, is constant or balanced Boolean function, besides, estimation of |α| and |β|. Although, this problem is very simple but it can not be solved using classical computers, because qubit can not be implemented physically using classical computers. A novel quantum algorithm based on principle of entanglement measure is proposed to solve this problem. IBMs 5-qubit quantum computer (ibmqx4) is used to realize the proposed algorithm experimentally.
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