We investigate the prospects of using two-mode intensity squeezed twin-beams, generated in Rb vapor, to improve the sensitivity of spectroscopic measurements by engaging two-photon Raman transitions. As a proof of principle demonstration, we demonstrated the quantum-enhanced measurements of the Rb $5D_{3/2}$ hyperfine structure with reduced requirements for the Raman pump laser power and Rb vapor number density.
We report quantum enhancement of Faraday rotation spin noise spectroscopy by polarization squeezing of the probe beam. Using natural abundance Rb in 100 Torr of N_2 buffer gas, and squeezed light from a sub-threshold optical parametric oscillator stabilized 20 GHz to the blue of the D_1 resonance, we observe that an input squeezing of 3.0 dB improves the signal-to-noise ratio by 1.5 dB to 2.6 dB over the combined (power)$\otimes$(number density) ranges (0.5 mW to 4.0 mW )$\otimes$(1.5 x 10^{12} cm^{-3} to 1.3 x 10^{13} cm^{-3}), covering the ranges used in optimized spin noise spectroscopy exp…
We measured the spin noise spectroscopy (SNS) of rubidium atomic ensemble with two different atomic vapor cells (filled with the buffer gases or coated with paraffin film on the inner wall), and demonstrated the enhancement of signal to noise ratio (SNR) by using of the polarization squeezed state (PSS) of 795 nm light field with Stokes operator S2 squeezed. PSS is prepared by locking the relative phase between the squeezed vacuum state of light obtained by a sub-threshold optical parametric oscillator and the orthogonal polarized local oscillator beam by means of the quantum noise lock. Under…
We investigate the prospect of enhancing the phase sensitivity of atom interferometers in the Mach-Zehnder configuration with squeezed light. Ultimately, this enhancement is achieved by transferring the quantum state of squeezed light to one or more of the atomic input beams, thereby allowing operation below the standard quantum limit. We analyze in detail three specific schemes that utilize (1) single-mode squeezed optical vacuum (i.e. low frequency squeezing), (2) two-mode squeezed optical vacuum (i.e. high frequency squeezing) transferred to both atomic inputs, and (3) two-mode squeezed opt…
Spin noise spectroscopy is emerging as a powerful technique for studying the dynamics of various spin systems also beyond their thermal equilibrium and linear response. Here, we study spin fluctuations of room-temperature neutral atoms in a Bell-Bloom type magnetometer. Driven by indirect pumping and undergoing a parametric excitation, this system is known to produce noise-squeezing. Our measurements not only reveal a strong asymmetry in the noise distribution of the atomic signal quadratures at the magnetic resonance, but also provide insight into the mechanism behind its generation and evolu…
With the help of Stokes operator S2 squeezed state (also called polarization squeezed state (PSS)) of 795-nm light, rubidium-87 (87Rb) atomic magnetometer based on Faraday rotation has been implemented and characterized.The PSS of Stokes operator S2 of 795-nm light has been prepared by means of coherently combining the polarization coherent state (PCS) of a linearly p-polarized bright 795-nm light beam and a linearly s-polarized squeezed vacuum state (SVS) generated by a 397.5-nm ultraviolet laser pumped sub-threshold optical parametric oscillator (OPO) with a PPKTP bulk crystal inside the OPO…
Laser intensity noise suppression has essential effects on preparation and characterization of the audio-frequency squeezed vacuum state of light based on a sub-threshold optical parametric oscillator (OPO).We have implemented two feedback loops by using relevant acousto-optical modulators (AOM) to stabilize the intensity of 795-nm near infrared (NIR) fundamental laser and 397.5-nm ultraviolet (UV) laser generated by cavity-enhanced frequency doubling.Typical peak-to-peak laser intensity fluctuation with a bandwidth of $\sim10$ kHz in a half hour has been improved from $\pm7.45$$\%$ to $\pm0.0…
Squeezed states of light have received renewed attention due to their applicability to quantum-enhanced sensing. To take full advantage of their reduced noise properties to enhance atomic-based sensors, it is necessary to generate narrowband near or on atomic resonance single-mode squeezed states of light. We have previously generated bright two-mode squeezed states of light, or twin beams, that can be tuned to resonance with the D1 line of $^{87}$Rb with a non-degenerate four-wave mixing (FWM) process in a double-lambda configuration in a $^{85}$Rb vapor cell. Here we report on the use of fee…
Generation of bright quantum high-order harmonic driven by combined coherent and bright squeezed vacuum light
Institute of Atomic and Molecular Physics, Jilin University（吉林大学原子与分子物理研究所）；Jilin Provincial Key Laboratory of Transient Quantum Process Control and Application, Jilin University（吉林大学瞬态量子过程控制与应用吉林省重点实验室）；College of Physics, Jilin University（吉林大学物理学院）
We study the fundamental limits of noise spectroscopy using estimation theory, Faraday rotation probing of an atomic spin system, and squeezed light. We find a simple and general expression for the Fisher information, which quantifies the sensitivity to spectral parameters such as resonance frequency and linewidth. For optically-detected spin noise spectroscopy, we find that shot noise imposes "local" standard quantum limits for any given probe power and atom number, and also "global" standard quantum limits when probe power and atom number are taken as free parameters. We confirm these estima…
The precision of a quantum sensor can overcome its classical counterpart when its constituents are entangled. In gaussian squeezed states, quantum correlations lead to a reduction of the quantum projection noise below the shot noise limit. However, the most sensitive states involve complex non-gaussian quantum fluctuations, making the required measurement protocol challenging. Here we measure the sensitivity of non-classical states of the electronic spin $J = 8$ of dysprosium atoms, created using light-induced non-linear spin coupling. Magnetic sublevel resolution enables us to reach the optim…
We study the generation of planar quantum squeezed (PQS) states by quantum non-demolition (QND) measurement of a cold ensemble of $^{87}$Rb atoms. Precise calibration of the QND measurement allows us to infer the conditional covariance matrix describing the $F_y$ and $F_z$ components of the PQS, revealing the dual squeezing characteristic of PQS. PQS states have been proposed for single-shot phase estimation without prior knowledge of the likely values of the phase. We show that for an arbitrary phase, the generated PQS gives a metrological advantage of at least 3.1 dB relative to classical st…
Coupled-resonance spectroscopy has been recently reported and applied for spectroscopic measurements and laser stabilizations. With coupled-resonance spectroscopy, one may indirectly measure some transitions between the excited states that are hard to be measured directly because of the lack of populations in the excited states. An improvement of the coupled-resonance spectroscopy by combining the technology of electromagnetically induced transparency (EIT) is proposed. The coupled-resonance spectroscopy signal can be significantly enhanced by EIT. Several experimental schemes have been discus…
We have investigated the benefits of spin squeezed states for clocks operated with typical Brownian frequency noise-limited laser sources. Based on an analytic model of the closed servo-loop of an optical atomic clock, we can give quantitative predictions on the optimal clock stability for a given dead time and laser noise. Our analytic predictions are in very good agreement with numerical simulations of the closed servo-loop. We find that for usual cyclic Ramsey interrogation of single atomic ensembles with dead time, even with the current most stable lasers spin squeezing can only improve th…
We have previously shown that quantum-enhanced atom interferometry can be achieved by mapping the quantum state of squeezed optical vacuum to one of the atomic inputs via a beamsplitter-like process [Phys.~Rev.~A \textbf{90}, 063630 (2014)]. Here we ask the question: is a better phase sensitivity possible if the quantum state transfer (QST) is described by a three-mode-mixing model, rather than a beamsplitter? The answer is yes, but only if the portion of the optical state not transferred to the atoms is incorporated via information recycling. Surprisingly, our scheme gives a better sensitivit…
We describe methods using frequency combs and optical resonators for recording two-dimensional (2D) ultrafast spectroscopy signals with high sensitivity. By coupling multiple frequency combs to higher-order modes of one or more optical cavities, background-free, cavity-enhanced 2D spectroscopy signals are naturally generated via phase cycling. As in cavity-enhanced ultrafast transient absorption spectroscopy (CE-TAS), the signal to noise is enhanced by a factor proportional to the cavity finesse squared, so even using cavities of modest finesse, a very high sensitivity is expected, enabling ul…
Using squeezed states it is possible to surpass the standard quantum limit of measurement uncertainty by reducing the measurement uncertainty of one property at the expense of another complementary property. Squeezed states were first demonstrated in optical fields and later with ensembles of pseudo spin-1/2 atoms using non-linear atom-light interactions. Recently, collisional interactions in ultracold atomic gases have been used to generate a large degree of quadrature spin squeezing in two-component Bose condensates. For pseudo spin-1/2 systems, the complementary properties are the different…
