scholarly journals Generation and Measurement of Squeezed Vacuum States at Audio-Band Frequencies

2019 ◽  
Vol 9 (7) ◽  
pp. 1272 ◽  
Author(s):  
Yinghao Gao ◽  
Jinxia Feng ◽  
Yuanji Li ◽  
Kuanshou Zhang
Keyword(s):  
Continuous Wave ◽  
Vacuum State ◽  
Local Oscillator ◽  
Fine Tuning ◽  
Vacuum Field ◽  
Single Frequency ◽  
Practical Applications ◽  
Phase Jitter ◽  
Squeezed Vacuum ◽  
Vacuum States

Squeezed vacuum states at audio-band frequencies are important quantum resources for practical applications. We demonstrated the generation of squeezed vacuum states at the audio-band frequencies from a subthreshold optical parametric oscillator with a periodically poled KTiOPO4 crystal pumped by a homemade continuous wave single-frequency dual-wavelength laser. To detect squeezed vacuum states at audio-band frequencies, the influences of the local oscillator (LO) power, the common mode rejection ratio (CMRR) of balanced homodyne detectors, and the phase jitter between the LO and squeezed vacuum field on the measurement of squeezed vacuum states at audio-band frequencies were considered. By optimizing the LO power, improving the CMRR of photodetectors to 67 dB based on the design of differential fine-tuning circuit and adjustable bias voltage, and reducing the phase jitter between the LO and squeezed vacuum field to 1.7° with the help of the coherent locking technique, 6.1 ± 0.3 dB squeezed vacuum states at audio frequencies from 5 kHz to 20 kHz were generated. A 3.0 ± 0.3 dB phase squeezed vacuum state was obtained at the audio frequency of 3.5 kHz.

scholarly journals A Local Oscillator Phase Compensation Technique for Ultra-Wideband Stepped-Frequency Continuous Wave Radar Based on a Low-Cost Software-Defined Radio

Sensors ◽  
2021 ◽  
Vol 21 (3) ◽  
pp. 780
Author(s):  
Kazunori Takahashi ◽  
Takashi Miwa
Keyword(s):  
Software Defined Radio ◽  
Initial Phase ◽  
Continuous Wave ◽  
Low Cost ◽  
Local Oscillator ◽  
The Other ◽  
Ultra Wideband ◽  
Single Frequency ◽  
Wave Radar ◽  
Stepped Frequency

The paper discusses a way to configure a stepped-frequency continuous wave (SFCW) radar using a low-cost software-defined radio (SDR). The most of high-end SDRs offer multiple transmitter (TX) and receiver (RX) channels, one of which can be used as the reference channel for compensating the initial phases of TX and RX local oscillator (LO) signals. It is same as how commercial vector network analyzers (VNAs) compensate for the LO initial phase. These SDRs can thus acquire phase-coherent in-phase and quadrature (I/Q) data without additional components and an SFCW radar can be easily configured. On the other hand, low-cost SDRs typically have only one transmitter and receiver. Therefore, the LO initial phase has to be compensated and the phases of the received I/Q signals have to be retrieved, preferably without employing an additional receiver and components to retain the system low-cost and simple. The present paper illustrates that the difference between the phases of TX and RX LO signals varies when the LO frequency is changed because of the timing of the commencement of the mixing. The paper then proposes a technique to compensate for the LO initial phases using the internal RF loopback of the transceiver chip and to reconstruct a pulse, which requires two streaming: one for the device under test (DUT) channel and the other for the internal RF loopback channel. The effect of the LO initial phase and the proposed method for the compensation are demonstrated by experiments at a single frequency and sweeping frequency, respectively. The results show that the proposed method can compensate for the LO initial phases and ultra-wideband (UWB) pulses can be reconstructed correctly from the data sampled by a low-cost SDR.

scholarly journals Measurement of the squeezed vacuum state by a bichromatic local oscillator

2015 ◽  
Vol 40 (22) ◽  
pp. 5299 ◽  
Author(s):  
Wei Li ◽  
Xudong Yu ◽  
Jing Zhang
Keyword(s):  
Vacuum State ◽  
Local Oscillator ◽  
Squeezed Vacuum State ◽  
Squeezed Vacuum

Superposition and entanglement of two-mode squeezed vacuum states

2018 ◽  
Vol 16 (01) ◽  
pp. 1850003 ◽  
Author(s):  
Amir Karimi
Keyword(s):  
Radiation Field ◽  
Vacuum State ◽  
Squeezed Vacuum ◽  
Vacuum States ◽  
Squeezing Operator ◽  
Parity Operator

In this paper, by using the parity operator as well as the two-mode squeezing operator, we define new operators which by the action of them on the vacuum state of the two-mode radiation field, superposition of two two-mode squeezed vacuum states and entangled two-mode squeezed vacuum states are generated.

scholarly journals DENSITY FLUCTUATIONS IN THE OSCILLATORY PHASE OF A NONCLASSICAL INFLATON IN THE FRW UNIVERSE

2008 ◽  
Vol 17 (11) ◽  
pp. 1991-2005 ◽  
Author(s):  
K. K. VENKATARATNAM ◽  
P. K. SURESH
Keyword(s):  
Vacuum State ◽  
Density Fluctuations ◽  
Einstein Equations ◽  
Semiclassical Theory ◽  
Squeezed State ◽  
Frw Universe ◽  
Squeezed Vacuum ◽  
Oscillatory Phase ◽  
Expansion Behavior ◽  
Vacuum States

The use of the coherent and squeezed state formalisms of quantum optics for a minimally coupled nonclassical inflaton in the FRW metric is studied, in the semiclassical theory of gravity. The leading order solutions to the semiclassical Einstein equations in the coherent, squeezed and squeezed vacuum states are obtained perturbatively and exhibit power law expansion behavior. The validity of the semiclassical theory is examined in the squeezed vacuum state in the oscillatory phase of the inflaton. The semiclassical theory in the oscillatory phase of the nonclassical inflaton holds only if the associated squeezing parameter is much smaller than unity. Quantum fluctuations of the inflaton are also examined in the coherent and squeezed state formalisms.

scholarly journals Continuous Human Activity Recognition through Parallelism LSTM with Multi-Frequency Spectrograms

2021 ◽  
Vol 13 (21) ◽  
pp. 4264
Author(s):  
Congzhang Ding ◽  
Yong Jia ◽  
Guolong Cui ◽  
Chuan Chen ◽  
Xiaoling Zhong ◽  
...  
Keyword(s):  
Activity Recognition ◽  
Human Activity ◽  
Continuous Wave ◽  
Short Term Memory ◽  
Human Activity Recognition ◽  
Living Environment ◽  
Single Frequency ◽  
Data Set ◽  
Practical Applications ◽  
Continuous Activities

According to the real-living environment, radar-based human activity recognition (HAR) is dedicated to recognizing and classifying a sequence of activities rather than individual activities, thereby drawing more attention in practical applications of security surveillance, health care and human–computer interactions. This paper proposes a parallelism long short-term memory (LSTM) framework with the input of multi-frequency spectrograms to implement continuous HAR. Specifically, frequency-division short-time Fourier transformation (STFT) is performed on the data stream of continuous activities collected by a stepped-frequency continuous-wave (SFCW) radar, generating spectrograms of multiple frequencies which introduce different scattering properties and frequency resolutions. In the designed parallelism LSTM framework, multiple parallel LSTM sub-networks are trained separately to extract different temporal features from the spectrogram of each frequency and produce corresponding classification probabilities. At the decision level, the probabilities of activity classification from these sub-networks are fused by addition as the recognition output. To validate the proposed method, an experimental data set is collected by using an SFCW radar to monitor 11 participants who continuously perform six activities in sequence with three different transitions and random durations. The validation results demonstrate that the average accuracies of the designed parallelism unidirectional LSTM (Uni-LSTM) and bidirectional LSTM (Bi-LSTM) based on five frequency spectrograms are 85.41% and 96.15%, respectively, outperforming traditional Uni-LSTM and Bi-LSTM networks with only a single-frequency spectrogram by 5.35% and 6.33% at least. Additionally, the recognition accuracy of the parallelism LSTM network reveals an upward trend as the number of multi-frequency spectrograms (namely the number of LSTM subnetworks) increases, and tends to be stable when the number reaches 4.

QUANTUM FLUCTUATION OF TWO-MODE SQUEEZED THERMAL VACUUM STATES AND THE THERMAL WIGNER OPERATOR STUDIED BY VIRTUE OF <η| REPRESENTATION

2001 ◽  
Vol 15 (12n13) ◽  
pp. 397-406 ◽  
Author(s):  
HONGYI FAN ◽  
HUI WANG
Keyword(s):  
Thermal Effect ◽  
Quantum Fluctuation ◽  
Vacuum State ◽  
Thermal Vacuum ◽  
Wigner Operator ◽  
Squeezed Vacuum State ◽  
Squeezed Vacuum ◽  
Thermo Field Dynamics ◽  
Vacuum States

Based on the <η| representation in Thermo Field Dynamics3 we introduce the thermal Wigner operator, with which we reach the conclusion that due to the thermal effect the quantum fluctuation of two-mode squeezed vacuum state increases by a factor cosh 2θ, where tanh θ = exp (-ℏω/2kT). We also mathematically analyse the formalism of Thermo Field Dynamics in the context of entanglement theory.

scholarly journals Generation of Coherent and Spatially Squeezed States of an Electromagnetic Beam in a Planar Inhomogeneous Dielectric Waveguide

Photonics ◽  
2019 ◽  
Vol 6 (3) ◽  
pp. 84 ◽  
Author(s):  
Anna Bogatskaya ◽  
Andrey Schegolev ◽  
Nikolay Klenov ◽  
Alexander Popov
Keyword(s):  
Single Mode ◽  
Waveguide Structure ◽  
Squeezed States ◽  
Practical Applications ◽  
Electromagnetic Beam ◽  
Squeezed Vacuum ◽  
Inhomogeneous Dielectric ◽  
Vacuum States ◽  
Mode Excitation ◽  
Index Gradient

We use slow-varying amplitude approximation (SVA) for the wave equation to study both analytically and numerically propagation of an electromagnetic beam in the waveguide structure with parabolic susceptibility spatial dependence. Such a structure is similar to the harmonic oscillator in quantum mechanics. We analyze this structure as a single mode guide and introduce the notion of number of “photons” in the mode. In particular, we pay special attention to the possibility of effective build-up of the coherent and spatially squeezed vacuum states of the mode that can be of interest for a number of practical applications. The way to provide these types of mode excitation is suggested. Several applications for controlling the mode composition of an electromagnetic wave in the parabolic index-gradient waveguide for various frequency ranges are considered.

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