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Strongly squeezed states at 532nm based on frequency up-conversion

Baune, C., Gniesmer, J., Schönbeck, A., Vollmer, C., Fiurasek, J., Schnabel, R.

Published Jan 1, 2015• 10 citations
OpenAlex

Abstract

Quantum metrology utilizes nonclassical states to improve the precision of measurement devices. In this context, strongly squeezed vacuum states of light have proven to be a useful resource. They are typically produced by spontaneous parametric down-conversion, but have not been generated at shorter wavelengths so far, as suitable nonlinear materials do not exist. Here, we report on the generation of strongly squeezed vacuum states at 532 nm with 5.5 dB noise suppression by means of frequency up-conversion from the telecommunication wavelength of 1550 nm. The up-converted states are employed in a model Mach-Zehnder interferometer to illustrate their use in quantum metrology.

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Quantum metrology utilizes nonclassical states to improve the precision of measurement devices. In this context, strongly squeezed vacuum states of light have proven to be a useful resource. They are typically produced by spontaneous parametric down-conversion, but have not been generated at shorter wavelengths so far, as suitable nonlinear materials do not exist. Here, we report on the generation of strongly squeezed vacuum states at 532 nm with 5.5 dB noise suppression by means of frequency up-conversion from the telecommunication wavelength of 1550 nm. The up-converted states are employed in a model Mach-Zehnder interferometer to illustrate their use in quantum metrology.
Quantum metrology utilizes nonclassical states to improve the precision of measurement devices. In this context, strongly squeezed vacuum states of light have proven to be a useful resource. They are typically produced by spontaneous parametric down-conversion, but have not been generated at shorter wavelengths so far, as suitable nonlinear materials do not exist. Here, we report on the generation of strongly squeezed vacuum states at 532 nm with 5.5 dB noise suppression by means of frequency up-conversion from the telecommunication wavelength of 1550 nm. The up-converted states are employed in a model Mach-Zehnder interferometer to illustrate their use in quantum metrology.
Quantum frequency conversion, the process of shifting the frequency of an optical quantum state while preserving quantum coherence, can be used to produce non-classical light at otherwise unapproachable wavelengths. We present experimental results based on highly efficient sum-frequency generation (SFG) between a vacuum squeezed state at 1064 nm and a tunable pump source at 850 nm ± 50 nm for the generation of bright squeezed light at 472 nm ± 4 nm, currently limited by the phase-matching of the used nonlinear crystal. We demonstrate that the SFG process conserves part of the quantum coherence as a 4.2(±0.2) dB 1064 nm vacuum squeezed state is converted to a 1.6(±0.2) dB tunable bright blue squeezed state. We furthermore demonstrate simultaneous frequency- and spatial-mode conversion of the 1064-nm vacuum squeezed state, and measure 1.1(±0.2) dB and 0.4(±0.2) dB of squeezing in the TEM01 and TEM02 modes, respectively. With further development, we foresee that the source may find use within fields such as sensing, metrology, spectroscopy, and imaging.
Squeezed states of light were observed for the first time in 1985.Since then they have developed into an important nonclassical tool in the field of high-precision metrology, for instance in gravitational wave detection, as well as in the field of quantum information, e.g. for teleportation and quantum cryptography.For all these applications a strong squeezing factor is beneficial.This thesis presents a new benchmark value for squeezed light from non-monolithic squeezed-light sources.By means of parametric down-conversion, squeezed states at a wavelength of 1064 nm were generated and a nonclassical noise suppression of 12.3 dB was observed.In contrast to a monolithic resonator, the resonance frequency of this squeezed-light source can be adjusted to a downstream experiment.In an additional experiment this squeezed-light source was utilized to determine the quantum efficiency of photo diodes.The applied method permits high precision since strong squeezing is sensitive to even low values of optical loss.In view of the application of squeezed light in future-generation gravitational wave detectors and quantum information science, a dedicated squeezed-light source was developed and at a wavelength of 1550 nm squeezing in the continuous-wave regime was observed for the first time.These squeezed states were employed to quantumenhance the sensitivity of a fiber-based Sagnac interferometer.Thus the compatibility of squeezing at 1550 nm with fiber-based quantum communication was demonstrated.Furthermore, upon thorough optimization of the squeezed-light generation and detection at 1550 nm, a quantum noise suppression of 12.3 dB was measured.Moreover, squeezing in the Fourier audio-band was observed for the first time.The findings presented in this thesis constitute key research towards the squeezed-light technology at 1550 nm as it is required for future gravitational wave detectors such as the recently proposed Einstein Telescope.
Squeezed vacuum states constitute a particularly useful resource in quantum information as well as in quantum metrology. The frequency conversion of these states is important to provide the bridge between different wavelengths within a sequence of downstream applications and also to provide a way for squeezed-state generation at so-far inaccessible wavelengths. Here we demonstrate the external quantum up-conversion of carrier-light-free squeezed vacuum states for the first time. Our result proves that nondegenerate sum-frequency generation preserves the coherences that are present between photon pairs and higher-order photon pairs of the squeezed input state.
Quantum frequency conversion, the process of shifting the frequency of an optical quantum state while preserving quantum coherence, can be used to produce non-classical light at otherwise unapproachable wavelengths. We present experimental results based on highly efficient sum-frequency generation (SFG) between a vacuum squeezed state at 1064 nm and a tunable pump source at 850 nm ±\pm± 50 nm for the generation of bright squeezed light at 472~nm ±\pm± 4~nm, currently limited by the phase-matching of the used nonlinear crystal. We demonstrate that the SFG process conserves part of the quantum coherence as a 4.2(±0.2\pm0.2±0.2)~dB 1064 nm vacuum squeezed state is converted to a 1.6($\pm0.2) dBtunablebrightbluesqueezedstate.Wefurthermoredemonstratesimultaneousfrequency−andspatial−modeconversionofthe1064−nmvacuumsqueezedstate,andmeasure1.1(0.2)~dB tunable bright blue squeezed state. We furthermore demonstrate simultaneous frequency- and spatial-mode conversion of the 1064-nm vacuum squeezed state, and measure 1.1(0.2) dBtunablebrightbluesqueezedstate.Wefurthermoredemonstratesimultaneousfrequency−andspatial−modeconversionofthe1064−nmvacuumsqueezedstate,andmeasure1.1(\pm0.2) dBand0.4(0.2)~dB and 0.4(0.2) dBand0.4(\pm0.2) dBofsqueezingintheTEM0.2)~dB of squeezing in the TEM0.2) dBofsqueezingintheTEM_{01}$ and TEM02_{02}02​ modes, respectively. With further development, we foresee that the source may find use within fields such as sensing, metrology, spectroscopy, and imaging.
Entanglement drives nearly all proposed quantum information technologies. By up-converting part of a 1550 nm two-mode squeezed vacuum state to 532 nm, we demonstrate the generation of strong continuous-variable entanglement between widely separated frequencies. Nonclassical correlations were observed in joint quadrature measurements of the 1550 and 532 nm fields, showing a maximum noise suppression 5.5 dB below vacuum. Our versatile technique combines strong nonclassical correlations, large bandwidth, and in principle, the ability to entangle the telecommunication wavelength of 1550 nm with any optical wavelength.