We report on experimental preparation of the second-harmonic-wave laser and the single-mode squeezed vacuum state of 795 nm (rubidium atom D1 line) with periodically-poled KTiOPO4 (PPKTP) bulk crystals. By using a four-mirror bow-tie type ring doubling cavity we achieved ~111 mW of continuous-wave single-frequency ultra-violet (UV) laser radiation at 397.5 nm with ~191 mW of 795 nm fundamental-wave laser input. The corresponding doubling efficiency is 58.1%. To our knowledge, this is the highest doubling efficiency at 795 nm so far. Employing the 397.5 nm UV laser as a pump source of an optical parametric oscillator (OPO) with a PPKTP crystal, we achieved 5.6 dB of 795 nm single-mode squeezed vacuum output at analyzing frequency of 2 MHz. To our knowledge, this is the highest squeezing level of 795 nm single-mode squeezed vacuum so far. We analyzed the pump power dependence of the squeezing level, and concluded that UV laser induced losses of PPKTP crystal are main limiting factors for further improving the squeezing level. The generated 795 nm vacuum squeezing has huge potential applications in quantum memory and ultra-precision measurement with rubidium atoms.
We report on experimental preparation of the second-harmonic-wave laser and the single-mode squeezed vacuum state of 795 nm (rubidium atom D1 line) with periodically-poled KTiOPO4 (PPKTP) bulk crystals. By using a four-mirror bow-tie type ring doubling cavity we achieved ~111 mW of continuous-wave single-frequency ultra-violet (UV) laser radiation at 397.5 nm with ~191 mW of 795 nm fundamental-wave laser input. The corresponding doubling efficiency is 58.1%. To our knowledge, this is the highest doubling efficiency at 795 nm so far. Employing the 397.5 nm UV laser as a pump source of an optical parametric oscillator (OPO) with a PPKTP crystal, we achieved 5.6 dB of 795 nm single-mode squeezed vacuum output at analyzing frequency of 2 MHz. To our knowledge, this is the highest squeezing level of 795 nm single-mode squeezed vacuum so far. We analyzed the pump power dependence of the squeezing level, and concluded that UV laser induced losses of PPKTP crystal are main limiting factors for further improving the squeezing level. The generated 795 nm vacuum squeezing has huge potential applications in quantum memory and ultra-precision measurement with rubidium atoms.
We report on efficient generation of second harmonic laser and single-mode vacuum squeezed light of 795 nm with periodically poled KTiOPO4 (PPKTP) crystals. We achieved 111 mW of ultra-violet (UV) light at 397.5 nm from 191 mW of fundamental light with a PPKTP crystal in a doubling cavity, corresponding to a conversion efficiency of 58.1%. Using the UV light to pump an optical parametric oscillator with a PPKTP crystal, we realized -5.6 dB of a maximum squeezing. We analyzed the pump power dependence of the squeezing level and concluded that the UV light induced losses limit the improvement of the squeezing level. The generated squeezed light has huge potential application in quantum memory and ultra-precise measurement.
We report the generation of a continuous-wave squeezed vacuum resonant on the Rb D1 line (795 nm) using periodically poled KTiOPO4 (PPKTP) crystals. With a frequency doubler and an optical parametric oscillator based on PPKTP crystals, we observed a squeezing level of -2.75+/-0.14 dB and an antisqueezing level of +7.00+/-0.13 dB. This system could be utilized for demonstrating storage and retrieval of the squeezed vacuum, which is important for the ultraprecise measurement of atomic spins as well as quantum information processing.
Squeezed states are important sources in quantum physics, which have potential applications in fields such as quantum teleportation, quantum information networks, quantum memory, and quantum metrology and precise measurements. For our interest, the squeezed vacuum will be used in the quantum-enhanced optical atomic magnetometers, filling the vacuum port of the probe beam to improve measurement sensitivity. Based on the sub-threshold optical parametric oscillator (OPO) with PPKTP crystal, the squeezed vacuum at rubidium D1 line of 795 nm is obtained. In our work, we investigate the noise sources in an OPO system. By carefully controlling the classical noise source, the squeezing band extends to the analysis frequency of 2.6 kHz. The flat squeezing trace is 2.8 dB below the shot noise limit. In our work, we focus on the difference between the squeezing results at the analysis frequency of kilohertz regime at two different wavelengths, 1064 nm and 795 nm. The difference mainly comes from the absorption of 795 nm laser and its second harmonic at 397.5 nm in crystal (397.5 nm laser is at the edge of transparent window of PPKTP crystal that has an absorption index much higher than at other wavelength). The absorption induced nonlinear loss and thermal instability greatly affect the squeezing results, which is discussed in our work. Squeezing level at 795 nm is worse than at 1064 nm due to the above-mentioned factors. Noise coupling to the detection system limits the squeezing band. In the audio frequency band, squeezing is easily submerged in roll-up noises and the measured squeezing level is limited. Two factors limit the obtained squeezing:the technical noise induced in the detection and the squeezing degradation by the noise coupling of the control beams. In experiment, we carefully control the classical noise at analytical frequency of kilohertz by means of a vacuum-injected OPO, a counter-propagating cavity locking beam with orthogonal polarization, low noise homodyne detector, stable experimental system and quantum noise locking method for squeezing phase locking. Firstly, to preclude the classical noise from coupling the laser source, we use the vacuum injected OPO. A signal beam helps optimize the parametric gain and is blocked in the squeezing measurement process. In order to maintain the OPO, a counter-propagating beam with orthogonal polarization is used for locking the cavity. Then, a low noise balanced homodyne detector with a common-mode rejection ratio of 45 dB helps improve the audio frequency detection. Finally, the quantum noise locking provides a method to lock the relative phase between the coherent beam and the squeezed vacuum field. With the combination of these technical improvements, a squeezed vacuum of 2.8 dB is obtained at the analysis frequency of 2.6-100 kHz. The obtained squeezing level is mainly limited by the relatively large loss in OPO, which is induced by ultra-violet absorption in PPKTP crystal. The generated squeezed field is used to reduce the polarization noise of probe beam in an optical magnetometer, in order to increase detection sensitivity.
We report the experimental generation of a squeezed vacuum at frequencies ranging from 2.5 kHz to 200 kHz that is resonant on the cesium D2 line by using a below-threshold optical parametric oscillator (OPO). The OPO is based on a periodically-poled KTiOPO 4 (PPKTP) crystal that is pumped using a bow-tie four-mirror ring frequency doubler. The phase of the squeezed light is controlled using a quantum noise locking technique. At a pump power of 115 mW, maximum quadrature phase squeezing of 3.5 dB and anti-squeezing of 7.5 dB are detected using a home-made balanced homodyne detector. This squeezed vacuum at an atomic transition in the kilohertz range is an ideal quantum source for quantum metrology of enhancing measurement precision, especially for ultra-sensitive measurement of weak magnetic fields when using a Cs atomic magnetometer in the audio frequency range.
The non-classical light resonance on the cesium D1 (894.6 nm) line has important applications in solid-state quantum information networks due to its unique advantages. The cesium D1 line has a simplified hyperfine structure and can be used to realize a light-atom interface. In our previous work, we demonstrated 2.8-dB quadrature squeezed vacuum light at cesium D1 line in an optical parametric oscillator(OPO) with a periodically poled KTP(PPKTP) crystal. However, the squeezing level is relatively low, and the tunability that has practical significance for squeezed light has not been further investigated. Theoretically, the increase of the transmittance of output mirror and the decrease of the intra-cavity loss of the OPO can improve the squeezing level. Here, we use super-polished and optimal coating cavity mirrors to improve the nonlinear process in OPO. We prepare 447.3 nm blue light from 894.6 nm fundamental light by a second harmonic generation cavity (SHG). The SHG is a two-mirror standing-wave cavity with a PPKTP crystal as the nonlinear medium. The power of generated blue laser is 32 mW when the incident infrared power is 120 mW. Using the blue light to pump an OPO, we achieve quadrature squeezed vacuum light at cesium D1 line. The OPO is a two-mirror standing-wave cavity with a PPKTP crystal. The threshold of OPO is reduced to 28 mW. The squeezing level of generated quadrature squeezed vacuum light is increased to 3.3 dB when the pump power is 15 mW. Taking into account the overall detection efficiency, the actual squeezing reaches 5.5 dB. We inject a weak signal beam into the OPO cavity to act as an optical parametric amplifier (OPA), and test the tunability of squeezzed light. The blue light and the squeezed light are tuned by using a low-frequency triangular wave signal to scan the Ti: sapphire laser. Gradually increasing the amplitude of the scanning triangle wave signal, the generated bright squeezed light can be continuously tuned over a range around 80 MHz without losing the stability of the whole system. The generated squeezed light offers the possibility for the efficient coupling between the non-classical source and solid medium in the process of quantum interface.
Abstract. We report on the generation of more than 5 dB of vacuum squeezed light at the Rubidium D1 line (795 nm) using periodically poled KTiOPO4 (PPKTP) in an optical parametric oscillator. We demonstrate squeezing at low sideband frequencies, making this source of non-classical light compatible with bandwidth limited atom optics experiments. When PPKTP is operated as a parametric amplifier, we show a noise reduction of 4 dB stably locked within the 150 kHz-500 kHz frequency range. This matches the bandwidth of Electromagnetically Induced Transparency (EIT) in Rubidium hot vapour cells under the condition of large information delay. Squeezed light at the Rubidium D1 line 2 The control of quantum states of light is of great interest for quantum communication purposes. Many quantum information protocols rely on the possibility of coherently delaying and storing the information carried by a laser beam. This can for example be achieved using Electromagnetically Induced Transparency (EIT). Experimental and theoretical studies have shown that information can be delayed within a narrow bandwidth when light interacts with atoms in a lambda configuration [2, 3, 4, 5]. One step further is the delay of quantum information, carried by squeezed