ObjectiveA phase-insensitive amplifier (PIA) based on atomic four-wave mixing is one of the ideal schemes for experimentally producing intensity-difference squeezed light. Improving its quantum properties is of great significance for the application of this non-classical light in the fields of quantum information and quantum precision measurement. By using a beam splitter as a feedback controller, the conjugated light from a PIA is partially fed back to the vacuum port, which can enhance the squeezing characteristics of its output intensity-difference squeezed light. This paper systematically investigates the dependence of the squeezing enhancement effect, induced by coherent feedback, on the physical parameters of the phase-insensitive amplifier. Our results indicate that in the ideal case of ignoring losses, infinite squeezing enhancement can be achieved by adjusting the reflectivity of the feedback controller. Under the parameter conditions of the actual experimental system, the PIA with coherent feedback can still realize significant squeezing enhancement. The research results can lay a theoretical foundation for the manipulation of the non-classical light field based on coherent feedback.MethodsThis paper focuses on the PIA based on the four-wave mixing process of 85Rb atoms. The conjugated light from a PIA is partially fed back to the vacuum port. Based on the input-output relationship of the PIA and a beam splitter, the noise formula of the output intensity-difference squeezed light is finally obtained. Based on this, the dependence of the squeezing characteristics on physical system parameters is explored.Results and DiscussionsBased on the noise formula, the dependence of intensity-difference squeezing form the PIA on feedback intensity, intensity gain, the absorption loss of the atomic vapor, and the optical loss of the feedback loop is numerically simulated and presented in the paper. The paper delves into the impact of feedback on controlling the non-classical properties of the output light field from the PIA, both in the ideal case of no loss and considering actual experimental parameters.ConclusionsIn an idealized scenario. the results indicate that infinite intensity-difference squeezing enhancement can be achieved by adjusting the feedback strength. For situations considering actual experimental parameters, significant squeezing enhancement can be achieved within a certain parameter range. It can be found that the squeezing enhancement effect is more pronounced at medium and low intensity gains, while the squeezing enhancement effect gradually weakens at high intensity gains. Our research results can provide a theoretical basis for the coherent feedback control of non-classical light fields, laying the foundation for their applications in quantum communication and quantum precision measurement fields.

ObjectiveSince the "Einstein-Podolsky-Rosen (EPR) paradox" was proposed by Einstein, Podolsky and Rosen in the early 20th century, quantum entanglement has become key to understanding non-local and non-classical correlations based on the quantum mechanics. The entangled sideband modes represent a vital quantum resource, enabling multi-channel, high-capacity quantum information processing by actively distributing sideband modes across multiple nodes within a quantum system. A large number of entangled sideband modes are generated through optical parametric down-conversion. However, the extraction and manipulation of vacuum sideband modes present significant challenges. Therefore, a simple sideband modes control scheme is needed desperately for easier integration and application.MethodsThis paper presents a frequency-comb-type seed beam injection control scheme to generate a coherent beam with the same frequency and convert the vacuum entangled sideband modes to bright optical modes. We employed a fiber-coupled wave-guide amplitude modulators (WGAM) based on Mach-Zehnder interferometer structure to generate the frequency-comb-type seed beam and the modulated frequency equals to the free spectral range of the optical parametric oscillator (OPO). By precisely adjusting the bias voltage of the WGAM, the 1st to 3rd sideband modes are simultaneously output. All of the modes are parametric amplification taking advantage of the phase-matching relationship in the OPO, which determined the signal to noise (SNR) of the squeezed angle locked error signal remains constant.The broadband squeezed state, which involves many EPR entangled modes at the symmetric sidebands of around the half-pump frequency, are generated by pumping the nonlinear crystal. The ring filter cavity (RFC) as the frequency beam splitter are utilized to separate the entangled sideband modes, the upper sideband modes resonate while the lower sideband modes reflect. The RFC is the near-impedance matching cavity, which could efficiently separate the sideband modes and reduce the decoherence. The separated sideband modes are interfered with the corresponding LOs on a 50/50 beam splitter and directed toward two pairs of balanced homodyne detectors (BHDs) to detect the correlation noise.Results and discussionsThe OPO is locked in the parametric amplification status for the entangled state controlling, in which the carrier and each order entangled sideband mode are amplified. Combined with efficient mode filtering, low-loss feedback control, and time-delay compensation techniques, we achieve stable control and efficient detection of entangled sideband modes. The optimal correlation noise variances of the first- to third-order entangled sideband modes are detected by employing narrowband and high-gain BHDs. The quadrature amplitude correlated noise variances are 7.8 dB, 7.8 dB, 7.7 dB, respectively, while the quadrature phase correlated noise variances are 7.8 dB, 7.6 dB, 7.5 dB. We also show the noise spectrum in 1～15 MHz frequency band of the multiple-orders entangled sideband modes.ConclusionsIn summary, we have experimentally demonstrated three pairs of entangled sideband modes by employing the frequency-comb-type seed beam injection scheme. The frequency-comb-type seed beam was generated by a waveguide amplitude modulator and then injected into OPO. By parametrically amplifying the three pairs of entangled sideband modes, the entangled sideband modes are actively controlled. This scheme provides a straightforward method for the control of sideband modes, which can be further applied to achieve the multi-channel multiplexing quantum communications.

ObjectiveQuantum logic gates serve as key components in realizing quantum computation, with high fidelity and robustness being directly linked to practical effectiveness. The geometric phase approach exhibits intrinsic resistance to local disturbances, offering unique advantages for efficient and stable quantum computing. Based on this, our study addresses error management in non-adiabatic geometric quantum gate operations, aiming to enhance gate fidelity through pulse design and parameter optimization, thereby achieving effective suppression of systematic errors.MethodsWe have established a theoretical framework for studying the robustness of non-adiabatic geometric quantum gates based on time-dependent perturbation theory. Using this framework, we analyzed the evolution of quantum gates and their responses to different types of errors. By deriving the expressions that quantify the impact of errors on fidelity, we proposed a new strategy for pulse design and parameter optimization based on an in-depth analysis of distinct error types.Results and discussionsOur results demonstrate that the proposed design significantly enhances the robustness and fidelity of quantum gates. Under the derived analytical conditions, our approach enables a simpler construction of quantum computing schemes and allows for rapid analysis of fidelity impacts from different errors. Additionally, we separated systematic errors based on the derived fidelity expressions, independently optimizing for detuning errors and Rabi errors. Through appropriate parameter selection and pulse design, we achieved second-order cancellation of Rabi errors in theory, maintaining high fidelity in complex environments. Numerical simulations further validated these results, demonstrating that this strategy yields clear fidelity advantages over conventional methods.ConclusionsThis study makes notable advances in pulse optimization for non-adiabatic geometric quantum gates, particularly in improving fidelity under Rabi error conditions. The proposed strategy, not dependent on strict pulse constraints, demonstrates broader applicability. This optimization approach not only provides an efficient solution for the current design of geometric quantum gates but also establishes a theoretical foundation for expanding their applicability and integration with other schemes in the future. Specifically, compared to some schemes in the literature, depending on the magnitude of the Rabi error, we can reduce the infidelity by 1 to 2 orders of magnitude. In conclusion, we developed a method to design pulses that are robust against systematic errors, particularly Rabi errors, while also being practical to implement experimentally.

ObjectiveThe thermal noise in the mirror coatings of a test mass is an important limiting noise source in high-precision measurements such as gravitational wave detection, and has become one of the main limitations of improving detection sensitivity. In order to improve the sensitivity of detection, it is necessary to adopt the thermal noise suppression technology, and even to adopt a combination of multiple non-interfering suppression techniques to reduce the thermal noise. So we combine the two suppression techniques of Khalili etalon (KE) with distributed reflective coating structure and high order Laguerre-Gaussian (LG) mode beam with wider and more uniform transverse intensity distribution compared to the base mode currently used.MethodsIn this paper, we calculated thermal noise based on the fluctuation-dissipation theorem. To calculate the thermal noise of the coating, the elastic equation of the substrate needs to be solved, and the coating thermal noise can be obtained by the boundary conditions between substrate and coatings. The boundary conditions for the substrate are determined according to the reflection of the beam in conventional mirror and KE respectively, and the beam intensity profile is expanded with the oscillation mode of test mass, which is described by the Bessel function. The strain and stress tensor and the elastic energy of substrate can be obtained from the elastic equation and boundary conditions, the three corresponding mechanical quantities of the coating are derived from deve the boundary conditions between the coatings and substrate. We add up the elastic energies of all the coatings to get the total coating thermal noise. The suppression factor is defined as the ratio of the original noise level to the noise level after suppression, and the distribution of the coating layers is determined by considering the factor and the absorption of substrate due to the reduction of the front coating layer.Results and DiscussionsCompared with the LG base mode currently used in aLIGO (Advanced laser interferometer gravitational wave observatory) and KAGRA (The Kamioka Gravitational Wave Detector), the high-order LG modes, which have a wider and more uniform light intensity distribution, can effectively average the fluctuation of the mirror surface to mitigate the influence of the Brownian motion of the mirror on the sensitivity of the detector. Since the suppression effects of the high-order mode and KE does not interfere with each other, they can be directly superimposed. We applied some high-order modes to the conventional mirror and KE while ensuring the equal diffraction loss, calculated the coating thermal noise of these modes. The suppression effect of the high-order mode on thermal noise increases as the order of the mode rises, but no mode is obviously better than other modes of same order. Considering the production efficiency of high-order modes and matching with the interferometer, we chose LG33 to demonstrate the suppression effect.ConclusionsAt the wavelength 1 550 nm of the laser light utilized in the third generation of gravitational-wave-detection laser interferometer, we combine with high-order LG33 mode and KE with 5 front coating layers to effectively suppress thermal noise at room temperature. The coating thermal noise is suppressed to 1/3 of the original level, which is equal to the thermal noise level when the test mass is cooled down to 30 K.

ObjectiveThe investigation of light-matter interaction through quantum control technology stands as a primary research focus in the field of atomic and molecular photon physics. Electromagnetically induced transparency (EIT) is a significant quantum interference phenomenon with crucial applications in optical deceleration, optical bistability, non-inversion lasers, and quantum information. Compared with the transition between atomic hyperfine energy levels, the magnetically induced transition (MIT) between atomic magneton energy levels can be regulated by the external magnetic field. The dark resonance signal with wide range and tunable narrow linewidth is obtained by changing the intensity of the external magnetic field and the frequency detuning of coupling laser, which is of great significance for wide-ranging laser frequency tuning and locking applications.MethodsThe dark resonance effect is investigated through the magnetically induced transitions of 85Rb atoms with the external magnetic field based on the -type energy level system of the D2 line. Theoretically, the relationship between the transition probability of different magnetically induced transitions and the magnetic field is calculated. Meanwhile, the dark resonance signal peak frequency with the magnetic field is obtained by calculating the density matrix. In the experiment, the probe laser is scanned near the transition frequency of 5S1/2 (Fg=3)-5P3/2 (Fe=1) with - circularly polarization, while the coupling laser is resonant at 5S1/2 (Fg=2, mF=0)-5P3/2 (Fe=1, mF=-1) transition with - circularly polarization. Finally, the magnetically induced transitions of 85Rb atoms 5S1/2 (Fg=3, mF=0)-5P3/2 (Fe=1, mF=-1) is excited under the magnetic field.Results and DiscussionsThe dark resonance signal peak corresponding to the magnetically induced transitions of 85Rb atoms is obtained when the magnetic field is 900 G, which is consistent with theoretical results. The dark resonance signal peak frequency exhibits the linear frequency shift in the negative detuning direction with the magnetic field increasing. The peak position of dark resonance signal shifts ～1.11 GHz when the magnetic field was gradually increased from 900 G to 1200 G in 50 G intervals. The result verifies the tunability of the dark resonance signal peak frequency. The dark resonance signal peak frequency exhibits the linear frequency shift in the positive detuning direction as frequency detuning of the coupling laser increasing. When the frequency detuning of the coupling laser gradually increases from 0 to 200 MHz in 40 MHz intervals, the peak position of dark resonance signal shifts ～0.25 GHz. These experimental results agree with the theoretical fitting results.ConclusionsThe experimental results indicate that the dark resonance signal peak position with controlled tuning is achieved by adjusting the external magnetic field and positive frequency detuning of the coupling laser. This work offers potential value for wide-range tunable laser frequency locking far from alkali metal atomic resonance transition positions.

As a basic model to describe strongly correlated Bose gases in lattice potential, the Bose-Hubbard model has been a hot topic in physics since it was proposed. The extension of the Bose-Hubbard model to a two-component coupled gas is straightforward and interesting. In particular, when the two components of bose gas experience completely different lattice potentials and interactions, the system will show very different properties from that of a single-component gas. Similarly, the interactions between itinerant and local particles in heavy fermion systems have been extensively studied, and a wealth of quantum phenomena have been discovered. So, what kind of novel phenomena will be produced by itinerant particles and local particles in the bosonic quantum system? In this paper, we consider the ground state properties of a two-component lattice boson system assisted by an optical cavity. In the vacuum environment, we assume that the two components of the bose gas are trapped in an optical lattice dependent on the spin internal states, where one component is completely local and the other is itinerant, and cavity photons can induce tunneling between the two components.In this work, variational method and self-consistent mean field approach are used to study the ground state properties of the system. These two methods have their own applicable scope and analytical advantages. In the case of the hard-core limit, the Hilbert space of the system is greatly reduced, and the analytical expression of the energy density of the system can be easily obtained by using the variational wave function, and the ground state properties of the system can be obtained by solving each parameter of the system through analytic calculation. However, in any real experimental system, the interactions between atoms are always finite, and the Hilbert space of the system is no longer restricted. In principle, the self-consistent mean field approach can deal with systems with arbitrary finite interaction strength. Utilizing the mean field decoupling approximation, we can study the quantum phase of the system by simply calculating the order parameters. By comparing the results of the two approaches, we can con-firm the reliability of the calculated results. Therefore, we divide this paper into two cases to fully study the ground state properties of the system, they are the hard-core limit case (the interaction is infinite) and the case where the interaction is finite, respectively.Utilizing the above two approaches, we systematically analyze the ground state properties of the system, and obtain the phase diagrams of the system in different parameter Spaces. The phase diagrams exhibit a wealth of quantum phases, including the Mott insulator phase, the superfluid phase, and the superradiant superfluid phase. We find that, with the help of cavity photons, the bosons of itinerant component can induce the quantum phase transition of the localized component from a Mott insulating phase to a superfluid phase. When the coupling strength of light and atom is nonzero, the average particle number per lattice site is closely related to specific quantum phases. In particular, the inter-component interaction may induce anomalous quantum phase transition between the Mott insulating and superradiant-superfluid phases in certain parameter regime. Finally, we provide a possible experiment implementation of our model. Our work enriches the physics of the Bose-Hubbard model and provides an instructive guidance for simulating condensed matter phenomena with ultracold atoms inside optical cavity.

ObjectiveNeutral atomic optical lattice clocks are based on the frequency transition of cold atoms trapped in the magic wavelength optical lattice as the frequency reference, and the frequency stability and uncertainty can reach the order of 10-19, which is a popular research in the field of time-frequency. The realization of the magic wavelength optical lattice with a reinforced cavity can greatly reduce the power requirement of the lattice laser. Cavity-enhanced optical lattice can achieve a large lattice waist with limited optical power, thereby significantly reducing the collision frequency shift between atoms. It also contributes to improve the transfer efficiency of cold atoms to the optical lattice and reduce the quantum projection noise.MethodsWe built a vacuum cavity-enhanced optical lattice system at magic wavelength for ytterbium optical clocks. Using the Pound-Drever-Hall (PDH) technique for laser frequency stabilization, we achieved accurate frequency control of 759 nm lattice laser as well as the enhancement cavity. The frequency noise of the enhancement cavity was evaluated by the error signal. We also analyzed the heating effect of the lattice on the trapped atoms, suppressed the heating effect by power stabilization, and then analyzed the lifetime of the optical lattice by monitoring the spectrum of transmitted signal intensity.Results and DiscussionsThe cavity enhancement factor reached 640 times. By measuring the intensity noise and power spectral density of the transmitted light in the cavity, we evaluated the lifetime of the optical lattice at different well depths, and the optical lattice lifetime can reach more than 10 seconds at a typical well depth of 10 μK.ConclusionsWe have built a vacuum cavity-enhanced optical lattice system for ytterbium atomic optical clocks which can use low-power, high-stability semiconductor lasers as lattice light sources, laying the foundation for further miniaturization and portability of atomic optical clocks.

ObjectiveIn strontium atomic optical clock experiments, hot atoms emitted from the Sr oven need to undergo precooling by a Zeeman decelerator and a transverse cooling device, which often results in a larger size for the optical clock system. To reduce the size of the optical clock system, we have integrated the Zeeman decelerator and transverse cooling device on the basis of ensuring the precooling effect.MethodsPreviously, we utilized 40 small magnets to design a permanent magnet array Zeeman decelerator with an overall length of 95 mm. By mounting three reflecting mirrors on the frame of the Zeeman decelerator, beam of 461 nm laser can create two pairs of mutually perpendicular transverse cooling beams across the cross-section of the decelerator, thereby achieving the integration of transverse cooling and the Zeeman decelerator. Furthermore, it was observed that at the axial magnetic field null point of the Zeeman decelerator, there exists a radial gradient magnetic field of approximately 27 G/cm. By installing reflecting mirrors at this location, a transverse cooling device based on a two-dimensional magneto-optical trap (2D MOT) can be constructed.Results and DiscussionsTo ensure the performance of the Zeeman deceleration, we simulated the motion of atoms within the Zeeman decelerator, calculated the proportion of low-speed atoms below 50 m/s, and compared it with experimental results. According to the simulation, transverse cooling can increase the proportion of low-speed atoms by a factor of 2.56. In the experiment, for hot atoms ejected from a Sr oven at 410 °C, the proportion of low-speed atoms was 0.5%. After the Zeeman deceleration process without transverse cooling, the proportion of low-speed atoms increased to 2.4%. Furthermore, after undergoing both Zeeman deceleration and transverse cooling processes, the proportion of low-speed atoms was further increased to 4.8%. This demonstrates that the 2D MOT-style transverse cooling device integrated within the decelerator can significantly enhance the effect of Zeeman deceleration.ConclusionsSince the transverse cooling device does not occupy separate space, we have reduced the size of the cold atomic beam source for strontium to 40 cm. Additionally, during the 560 ms loading period, the first cooling stage captured 8.0×10587Sr atoms. The design that integrates a 2D MOT-style transverse cooling device into the Zeeman decelerator is of significant importance for the realization of high-performance, compact strontium atomic optical clocks.

ObjectiveThis paper aims to investigate the impact of Pauli blocking on photon scattering within ultracold Fermi gases, with a specific focus on elucidating the role of Fermi statistics in these scattering processes. This research endeavors to provide novel insights into the quantum effects governing the interaction between light and matter, thereby enhancing our understanding of these fundamental phenomena.MethodsIn the experimental, ultracold 6Li Fermi gases with a spin mixture of two hyperfine states were prepared. Probe light was applied to the atoms in the horizontal direction. By collecting and detecting photons scattered by the atoms, changes in the scattered light were observed. The temperature of the atomic ensemble was modulated by closing and then reopening the far-detuned optical dipole trap. The imbalance between the two hyperfine states was controlled by adjusting the duration of radio frequency (RF) pulses. The impact of Pauli blocking on photon scattering under various conditions was systematically studied.Results and discussionsThe experimental results demonstrate that at low temperatures, when the atom numbers of the two components are nearly equal, Pauli blocking exerts a significant suppression on photon scattering, resulting in an extremely weak scattered light signal. Conversely, when the atom number ratio of the two components becomes imbalanced, the Pauli blocking effect becomes pronounced, allowing most of the probe light to pass through the Fermi gas without being absorbed or scattered. This observation underscores the pivotal role of Pauli blocking in the interaction between light and atoms.ConclusionsThis paper experimentally confirms the suppression of photon scattering due to the Pauli blocking effect in ultracold Fermi gases, providing new experimental data that enhances our understanding of the interaction between Fermi gases and light. Furthermore, this study lays the groundwork and provides valuable insights for future explorations into the coupling between light and atomic pairing, thereby advancing the field of quantum optics and condensed matter physics.

ObjectiveSurface plasmon Polariton (SPP) can bind the light field in a region far smaller than its free space wavelength, which is a technique that can break the diffraction limit and help to reduce the size of optical devices. Since SPP has obvious advantages at deep subwavelength scales, it is regarded as the key to manipulating optical signals at subwavelength scales. Terahertz (THz) waveguides are the basic components for the construction of various terahertz functional devices, which is of great significance for the realization of on-chip terahertz functional devices and ultra-wideband terahertz communication in the future. The surface conductivity of graphene is almost pure imaginary at the terahertz band, and it can exhibit properties similar to metal materials, so it can be regarded as a very thin metal layer, and the graphene plasmons also has low loss, strong confinement and tunability. However, in the terahertz band, although SPP has a long propagation length and low transmission loss, due to the difficult to adjust the properties of metal materials, its binding on the metal surface is still weak, so it is still difficult to achieve the effect of compact photon integration. A hole-based graphene hybrid plasmonic waveguide is proposed. By adjusting the parameters and the chemical potential of graphene, the mode characteristics and transmission characteristics of the hybrid mode are studied numerically. Compared with the hybrid waveguide without air hole, the hybrid waveguide has strong binding and low loss, which is more conducive to photon integration and achieves better transmission performance. In addition, the crosstalk characteristics between the two hybrid plasma waveguides are also studied to further achieve ultra-low crosstalk. The low crosstalk characteristics of this structure will have broad development prospects in future terahertz integrated circuits.MethodsThe characteristic patterns of the hole-based graphene hybrid plasmonic waveguide system with different structural parameters and chemical potential of graphene are calculated by finite element analysis method. In the process of analysis, it is assumed that the calculation region in x-direction and y-direction is infinite to ensure accurate eigenvalues. The mode effective index and propagation length are determined by the real and imaginary parts of the eigenvalue, respectively.Results and DiscussionsThe proposed hole-based graphene hybrid plasmonic waveguide optimizes the transmission characteristics of the hybrid waveguide by changing the gap height, the size of air hole and the chemical potential of graphene. Firstly, we discuss the effect of the side length of air hole on the mode characteristics of basic hybrid plasma guided by hole-based graphene hybrid plasmonic waveguide. When the side length of air hole increases from 15 m to 19 m, the normalized mode area Aeff/A0 is as small as 2.77×10−4, the corresponding propagation length is 21.8 m, and the figure of merit is 38.7. Secondly, we discuss the effect of gap height on the mode properties of the basic hybrid plasma. The gap height is reduced from 2.5 m to 0.5 m, the normalized mode area Aeff/A0 is as small as 2.77×10−4, the corresponding propagation length is 21.8 m, and the figure of merit is 38.7. Thirdly, we discuss the effect of the chemical potential of graphene on the mode properties of the basic hybrid plasma. The variation range of the chemical potential of graphene is changed between 0.4 eV and 1 eV, and the side length of air hole is increased from 15 m to 19 m, the normalized mode area Aeff/A0 is as small as 2.77×10−4, the corresponding propagation length is 21.8 m, and the figure of merit is 38.7. When the change range of the chemical potential of graphene is controlled between 0.4 eV and 1 eV, and the gap height is reduced from 2.5 m to 0.5 m, the normalized mode area Aeff/A0 is as small as 2.77×10−4, the corresponding propagation length is 21.8 m, and the figure of merit is 38.7. Finally, the crosstalk between two hole-based graphene hybrid plasmonic waveguides could be reduced to 22 m by changing the structural parameters and the chemical potential of graphene.ConclusionsThe research findings indicate that the proposed structure can reduce the normalized mode field area to 2.77×10−4, which is more conducive to photon integration and achieves better transmission performance. In addition, the crosstalk of two hybrid plasma waveguides, i.e., the minimum critical value of the center distance between waveguides without crosstalk, are reduced to 22 m. These results contribute to a deeper understanding of characteristics graphene-dielectric hybrid plasmonic waveguide, which provide important references for the design and optimization ultra-low crosstalk hybrid plasma waveguides. The proposed structure will have broad development prospects in future terahertz integrated circuits.

ObjectiveIn the research of organic light-emitting devices (OLEDs), the spin mixing process is of great significance as it closely relates to device performance. In order to deeply investigate the effect of exciton concentration on the spin mixing process in organic light-emitting devices, the bulk heterojunction devices with the structure of ITO/MoO3(5 nm)/NPB(30 nm)/NPB: Alq3(1:x, 70 nm)/Alq3(40 nm)/CsCl(0.6 nm)/Al(120 nm) [x=1, 2, 3, 4] are fabricated.MethodsThe optoelectronic properties and organic magnetic effects of the devices are studied at room temperature by utilizing the photo-electro-magnetic techniques. By applying these techniques, we can accurately obtain and analyze various parameters related to the devices' performance, such as current-voltage characteristics, light-emitting intensity under different magnetic fields, and the changes in these parameters with respect to different doping concentrations and bias voltages.Results and DiscussionsWe find that both the Magneto-Conductance (MC) and Magneto-Electroluminescence (MEL) curves of the devices are enhanced with increasing the doping concentration of Alq3 under the same bias voltage at room temperature, among them increase by 1.4%. This indicates a strong correlation between the doping concentration and the performance metrics related to spin-dependent transport and light emission. Moreover, the amplitude of MC and MEL curves are reduced with increasing the bias voltage when the doping ratio remains unchanged. Additionally, the effect of temperature on the MEL curves of the devices is further investigated. The line-shape of the MEL curves are distinctly modulated with decreasing temperature, involving that the MEL curves within low magnetic field ranges increase rapidly, while that within high magnetic field ranges first increase slowly to decrease.ConclusionsThese experimental results are deeply analyzed by considering the intersystem crossing (ISC), triplet-triplet annihilation (TTA), and triplet-charge annihilation (TCA) mechanisms. We demonstrated that the exciton concentration can be effectively adjusted by modifying the doping ratio to further improve the optoelectronic properties and organic magnetic effects of the device. This work provides a reliable basis for designing the high-performance bulk heterojunction organic light-emitting devices by modulating the complex spin mixing process.

ObjectiveBalanced photodetectors are a kind of high-sensitivity, low-noise photodetectors with two optical signal receivers, and the output signal is proportional to the difference between the two input optical powers. Owing to the differential detection technique, balanced photodetectors can effectively suppress common-mode noise, greatly improving the sensitivity and signal-to-noise ratio (SNR) of the optoelectronic system. Balanced photodetectors have been widely used in the fields such as laser coherent detection, coherent optical communication, and quantum optics. The performance parameters such as bandwidth, conversion gain, and noise equivalent power (NEP) of balanced photodetectors are mainly determined by the transimpedance amplifier (TIA). OPA847 and OPA657 produced by Texas Instruments are two high-speed, low-noise operational amplifiers that are suitable for implementing TIA and are widely used in commercial photodetectors and related research. Studying the performance of the TIAs based on OPA847 and OPA657 has important reference significance for designing different types of balanced photodetectors.MethodsThis paper theoretically and experimentally studies the bandwidth and noise characteristics of balanced photodetectors based on TIAs with OPA847 and OPA657. The dependence of the −3 dB bandwidth and the NEP of the balanced photodetectors on the transimpedance gain of TIA is theoretically calculated by using the equivalent circuit and noise model of photodiodes and TIA. The performance difference between the OPA847- and OPA657-based TIAs are compared. The contributions of the voltage and current noises of the operational amplifier and the thermal noise of the feedback resistor to the NEP are analyzed in detail. The balanced photodetectors based on OPA847 and OPA657 with transimpedance gains of 2 kV/A and 200 kV/A are experimentally performed, and their frequency and noise performances are measured. The −3 dB bandwidth is obtained from the frequency response and the NEP is obtained from the noise power spectrum. The measured −3 dB bandwidth and the NEP are compared with the theoretical values. The noise figure (NF) of the secondary voltage amplifier is evaluated from the TIA and the total noise power spectra. In additional, the noise power spectra of the balanced photodetectors at different local-oscillator powers are measured.Results and DiscussionsThe theoretical calculations show that OPA847 leads to a smaller NEP for a lower transimpedance gain and a larger bandwidth, while OPA657 leads to a smaller NEP for a higher transimpedance gain and a smaller bandwidth. In experiment, for the transimpedance gain of 2 kV/A, OPA847 and OPA657 give rise to −3 dB bandwidths of 220 MHz and 130 MHz, and NEPs of 8.2pW/Hz and 22pW/Hz, respectively. For the transimpedance gain of 200 kV/A, they give rise to −3 dB bandwidths of 9.2 MHz and 8.5 MHz, and NEPs of 4.3pW/Hz and 2.3pW/Hz, respectively. All the four configurations of the balanced photodetectors achieve common-mode rejection ratios (CMRRs) greater than 30 dB within the −3 dB bandwidth range. A shot-noise measurement of 10 dB-higher than electronic noise is achieved within the saturation power range for these balanced photodetectors. The theoretical and experimental studies demonstrate that OPA847 is suitable for achieving large-bandwidth, low-noise balanced photodetectors, while OPA657 is suitable for achieving high-gain, low-noise balanced photodetectors.ConclusionsThis paper presents a study on the frequency and noise characteristics of the balanced photodetectors based on TIAs with OPA847 and OPA657. The dependence of −3 dB bandwidth and the NEP on the transimpedance gain of TIA is calculated, and the performance advantages of OPA847 and OPA657 at low and high transimpedance gains are analyzed. The balanced photodetectors with transimpedance gains of 2 kV/A and 200 kV/A are experimentally implemented based on OPA847 and OPA657, respectively. The frequency response, noise power spectrum, CMRR and NEP are measured. Furthermore, the noise power spectra at different local-oscillator powers are measured, and the optical power and frequency range where the shot noise is 10 dB higher than the electronics noise are given. The results show that OPA847 and OPA657 are suitable for implementing high-bandwidth and large-gain balanced photodetectors, respectively. This research provides important reference significance for selecting suitable operational amplifiers in the design of different types of balanced photodetectors.