Entangled microwave signal is a new quantum information resource generated in recent years. We present that entangled microwave signals can be used as the medium to realize quantum information transmission. Focusing on the divergent problem of propagation, a partial detection model based on beam splitter is established to investigate the detection efficiency and influence factors of entangled microwave signals. We analyze the relation between the entanglement degree of partial detection and detection ratio and discuss the reason that causes the reduction of entanglement degree. We give ameliorative designs of microwave signal generator and transmitter to increase the operating distance and pave the way for the application of entangled microwave signals.
Entangled microwave signal is a new quantum information resource generated in recent years. We present that entangled microwave signals can be used as the medium to realize quantum information transmission. Focusing on the divergent problem of propagation, a partial detection model based on beam splitter is established to investigate the detection efficiency and influence factors of entangled microwave signals. We analyze the relation between the entanglement degree of partial detection and detection ratio and discuss the reason that causes the reduction of entanglement degree. We give ameliorative designs of microwave signal generator and transmitter to increase the operating distance and pave the way for the application of entangled microwave signals.
In recent years, the great progress of studying the quantum entanglement has been made. In the field of optics, the great success has been achieved in quantum entanglement theory and technology. Then researchers concentrate on the microwave frequency band whose frequency is lower than that of optical frequency band. The signal in the microwave frequency band has a longer wavelength, and it has the diffraction capability that the optical signal does not possess. Furthermore, it can spread further in complex environments. Now it is possible to experimentally produce squeezed state of microwave signals and spatially separated path-entangled microwave signals. It is an important issue to judge whether the microwave signals received through dual paths are in entanglement state. In this paper, we firstly introduce the method of using squeezed state of microwave and microwave beam splitter to prepare path-entangled microwave signals. Then we use entanglement witness method to detect entanglement. Through constructing the entanglement witness operator in path-entangled microwave signals, the entanglement of path-entangled microwave signals can be effectively detected. We decompose the expression of the continuous variables path-entangled microwave signals into a large number of 2 2 entangled superposition states, deduce an entangled witness operator of path-entangled microwave signals based on the principle of partial transpose criterion and entanglement witnessing, and prove that the entangled witness can be used to detect the path-entangled microwave signals. Finally, we propose a physical verification of path-entangled microwave signal entanglement. The verification can be realized as follows:firstly, we reverse the phase of a received quantum-state microwave signal by utilizing continuous variable controlled phase gate in a range of 0-, then we send two microwave signals into the two input ports of the microwave beam splitter, and we operate coincidence counting of microwave photons on the two output ports after entanglement microwave signals have passed through the microwave splitter. By analyzing the results of the whole process, we have the following conclusions:if the coincidence rate of two input signals is higher than that of non-entangled microwave signals under the same power, signals can be counted as entanglement. The proposed method can detect the entangled microwave signals more efficiently than the conventional methods, such as quantum state reconstruction, and thus reduce the detection and computational complexity. The entanglement of the two microwave quantum state signals can be observed directly by using this method. This paper provides a new idea for detecting the path-entangled microwave signals.
The entangled state of continuous variables of microwave frequency is an important resource in the field of quantum. In order to apply it to quantum communication protocol and quantum radar, the entanglement between two spatially separated subsystems, namely dual-path entangled quantum microwave is needed. However, for the circuit that generates the entangled quantum microwave, there is no suitable method to indicate whether the quality of the entangled microwave signal is good or not. Aiming at this problem, we put forward a method of evaluating the quality of dual-path entangled quantum microwave signals generated based on von Neumann entropy. The origin of the entangled quantum microwave is that vacuum state signals are transformed into squeezed state signals in driven pump, so in this paper we use a two-mode squeezed vacuum state to describe the formation of dual-path entangled quantum microwave signal, thus providing the function relation between the photon number and the squeezed parameter. In a communication system, the signal-noise ratio is usually used to express the reliability of system. Entropy is a measure of disorder degree in information. If both of them can be made the analogy, the entropy is used to evaluate the proportion of entangled state signals, the quality of original signals will be evaluated and the relationship among the entropy and squeezed parameter and the photon number will be analyzed. The simulation results show that the photon number in the entangled quantum microwave signal is determined by the squeezed parameter, and there is an index change with the square rule between them. Entropy decreases with the increase of squeezed parameter: its minimum value is 0, and its maximum value can be found from 0.9 to 1. The slope of curve is steep near the maximum, which reflects that the influence of squeezed parameter on the degree of entanglement is obvious, and that the range of optimal value choices in squeezed parameter is very narrow. The optimal value of squeezed parameter is dependent on photon number; it increases with the increase of the photon number. Entropy tends to decrease smoothly with the increase of squeezed parameter and it approximately has a negative exponent relation. The photon number in an actual signal is limited, so the limit value of entropy is estimated to be about 65%. The research shows that the quality of the entangled microwave signal can be improved by choosing appropriate squeezed parameter in different circuits that generate dual-path entangled quantum microwave signals for meeting the actual needs. Therefore, the research can provide the method of choosing the parameters of dual-path entangled quantum microwave circuit and improve the availability of system.
The generation and detection of dual-path entangled quantum microwave are widely investigated in recent years. Nevertheless, entangled quantum microwave is usually expressed and processed in quantum frame. In order to observe the entangled information and apply it to some fields, we also need to measure it and transform it into the form of electric signals. Therefore, we investigate the time domain waveform of dual-path entangled microwave signals from the view of measurement. In different measurement interval, the waveform of one-path entangled microwave signal is completely random. While the waveforms of two-path entangled microwave signal always meet the relationship of positive correlation or negative correlation. The randomicity and correlativity is the most intrinsic characteristic of entangled microwave signals. By analyzing the relation of mean value, fluctuation, entangled photon number and squeezed parameter, we explain the essence of the quantum stochastic and correlated characteristics in physics. A more intuitive understanding of entangled microwave signals would be felt in this research, which makes us easier to utilize the characteristic for the potential applications.
Quantum sensing is a creative application of quantum technology which is opening new horizons in order to make sensitive measurements even below the Standard Quantum Limit (SQL). In order to achieve this, an exclusive phenomenon of Quantum Entanglement is widely used for various tasks such as target detection, providing high resolution of the target, encryption of data and quantum teleportation which may seem to be impracticable. Moreover, the field of quantum technology has witnessed appreciable progress by using microwaves than optical photons. Microwave photons as efficient they are can also be used in a system for obtaining quantum information about the surroundings. \nIn this work, an idea is proposed to make use of microwaves as a source for the photonic sensor network. Squeezed microwave states are used for the generation of microwave photons which are used in their entangled state distributed among sensors and thereafter detected by the homodyne detector. Here, the use of hybrid coupler is also made to act as beam splitters forming the Continuous Variable multipartite entanglement of the microwave photons for further detection. Another idea is proposed to use a system for generation and detection of microwave photons in order to have application in quantum sensing field. In this for the generation part Nitrogen Vacancy (NV) centers defect is used as these NV centers with electrons can be used to manipulate microwaves in order to emit photons which carry quantum information about the environment. Then these emitted photons can be detected using a system formed by qubits and resonators which are coupled in a peculiar way using the dissipation engineering to detect itinerant photons.
Path entanglement constitutes an essential resource in quantum information and communication protocols. Here, we demonstrate frequency-degenerate entanglement between continuous-variable quantum microwaves propagating along two spatially separated paths. We combine a squeezed and a vacuum state using a microwave beam splitter. Via correlation measurements, we detect and quantify the path entanglement contained in the beam splitter output state. Our experiments open the avenue to quantum teleportation, quantum communication, or quantum radar with continuous variables at microwave frequencies.