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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Periodically poled KTP based High Efficiency Second Harmonic Generation of Cesium D2 line for Atomic Quantum Memory experiments

A. Chiummo, Fabrizio Villa, J. Cviklinski, J. Ortalo, E. Giacobino, Alberto Bramati

Published Jun 1, 2007• 0 citations
Publisher

Abstract

Summary form only given. One of the major objectives in the field of quantum information is the realization of a memory for the quantum states of the light. The squeezed vacuum is required in order to test the quantum character of the memory i.e. its capability to store informations that rely on the quantum nature of the light. In order to generate the squeezed vacuum at a wavelength that is resonant with the elected atomic transition, we adopt an experimental configuration that consists in a continuous wave subthreshold frequency degenerate optical parametric oscillator (OPO) pumped by a frequency doubled Ti:Sa laser. we achieve more than 300 mW stable blue-light at 426 nm; that is, to the best of our knowledge, the highest power obtained to date at this wavelength.

DOI
10.1109/cleoe-iqec.2007.4386082

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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•Jun 1, 2007•0 citations
Summary form only given. One of the major objectives in the field of quantum information is the realization of a memory for the quantum states of the light. The squeezed vacuum is required in order to test the quantum character of the memory i.e. its capability to store informations that rely on the quantum nature of the light. In order to generate the squeezed vacuum at a wavelength that is resonant with the elected atomic transition, we adopt an experimental configuration that consists in a continuous wave subthreshold frequency degenerate optical parametric oscillator (OPO) pumped by a frequency doubled Ti:Sa laser. we achieve more than 300 mW stable blue-light at 426 nm; that is, to the best of our knowledge, the highest power obtained to date at this wavelength.
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.
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.
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 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.
In this experiment we use periodically poled potassium titanyl phosphate (PPKTP) as the nonlinear crystal in an optical parametric oscillator (OPO) for the generation of squeezed light on the D1 line of rubidium which lies at 795 nm. Although OPOs have long been used as sources of squeezed light, the shorter wavelengths required for atomic interactions have always been a challenge due to a limited choice of nonlinear crystals. PPKTP is a new material that has recently been shown to be highly effective over a very wide range of optical frequencies (Akamatsu, 2006).