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arXiv:0909.5386 · Physical Review A

Observation of squeezed states with strong photon-number oscillations

Moritz Mehmet, H. Vahlbruch, N. Lastzka, K. Danzmann, Roman Schnabel

Published Jan 21, 2010• 146 citations
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Abstract

Squeezed states of light constitute an important nonclassical resource in the field of high-precision measurements, for example, gravitational wave detection, as well as in the field of quantum information, for example, for teleportation, quantum cryptography, and distribution of entanglement in quantum computation networks. Strong squeezing in combination with high purity, high bandwidth, and high spatial mode quality is desirable in order to achieve significantly improved performances contrasting any classical protocols. Here we report on the observation of 11.5 dB of squeezing, together with relatively high state purity corresponding to a vacuum contribution of less than 5%, and a squeezing bandwidth of about 170 MHz. The analysis of our squeezed states reveals a significant production of higher-order pairs of quantum-correlated photons and the existence of strong photon-number oscillations.

DOI
10.1103/physreva.81.013814

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Squeezed states of light constitute an important nonclassical resource in the field of high-precision measurements, for example, gravitational wave detection, as well as in the field of quantum information, for example, for teleportation, quantum cryptography, and distribution of entanglement in quantum computation networks. Strong squeezing in combination with high purity, high bandwidth, and high spatial mode quality is desirable in order to achieve significantly improved performances contrasting any classical protocols. Here we report on the observation of 11.5 dB of squeezing, together with relatively high state purity corresponding to a vacuum contribution of less than 5%, and a squeezing bandwidth of about 170 MHz. The analysis of our squeezed states reveals a significant production of higher-order pairs of quantum-correlated photons and the existence of strong photon-number oscillations.
Squeezing of light's quantum noise requires temporal rearranging of photons. This again corresponds to creation of quantum correlations between individual photons. Squeezed light is a nonclassical manifestation of light with great potential in high-precision quantum measurements, for example, in the detection of gravitational waves [C. M. Caves, Phys. Rev. D 23, 1693 (1981)10.1103/PhysRevD.23.1693]. Equally promising applications have been proposed in quantum communication [H. P. Yuen and J. H. Shapiro, IEEE Trans. Inf. Theory 24, 657 (1978)10.1109/TIT.1978.1055958]. However, after 20 years of intensive research doubts arose whether strong squeezing can ever be realized as required for eminent applications. Here we show experimentally that strong squeezing of light's quantum noise is possible. We reached a benchmark squeezing factor of 10 in power (10 dB). Thorough analysis reveals that even higher squeezing factors will be feasible in our setup.
Non-classical squeezed states of light are becoming increasingly important to a range of metrology and other quantum optics applications in cryptography, quantum computation and biophysics. Applications such as improving the sensitivity of advanced gravitational wave detectors and the development of space-based metrology and quantum networks will require robust deployable vacuum-compatible sources. To date non-linear photonics devices operated under high vacuum have been simple single pass systems, testing harmonic generation and the production of classically correlated photon pairs for space-based applications. Here we demonstrate the production under high-vacuum conditions of non-classical squeezed light with an observed 8.6 dB of quantum noise reduction down to 10 Hz. Demonstration of a resonant non-linear optical device, for the generation of squeezed light under vacuum, paves the way to fully exploit the advantages of in-vacuum operations, adapting this technology for deployment into new extreme environments.
Recently, the strong single-mode squeezed vacuum state of light with −15-15−15−15 dB of classic noise has been created [Phys. Rev. Lett.117, 110801 (2016)10.1103/PhysRevLett.117.110801]. This is an important resource in continuous variable (CV) quantum communication and fault-tolerant quantum computing. Nevertheless, strong squeezing means a non-negligible population in high-photon-number subspace and may pose a strong challenge to photon-based technology, for example, entanglement distillation. Entanglement distillation is an efficient method for retrieving a higher quality of entanglement from a weakly entangled state. Up till now, almost all the schemes for entanglement distillation are restricted to the low-squeezing regime. The distillation of strong-squeezing induced entanglement is an interesting but open topic in the near future. Here, we take the single-mode squeezed entangled state (SMSE) as an example and show that conventional photon subtraction based distillation fails to generate a higher quality of entanglement with experimentally feasible optical beam splitters. To this point, we show that the superposition of photon annihilation and creation could be an effective method. A practical scheme for implementing such a superposition with on-line squeezing is suggested. Our method is verified numerically by the calculation of a 25 dB SMSE state with an ideal photon detector and for distillation of 20.5 dB SMSE state with practical dichotic on-off detectors. The analysis of the distillation of the strong squeezing effect could be extended straightforwardly to other squeezing-based quantum information processing, such as quantum metrology and quantum illumination.
Squeezed states of light and entangled photon source are fundamental resources for quantum science and technology, enabling advances in quantum communication, computation, and precision metrology. Here, we experimentally demonstrate the generation of ultrabright squeezed vacuum and entangled photon pairs via type-I high-gain parametric down-conversion. Using femtosecond pump pulses at 1,030 nm, we produce ultrabright squeezed vacuum with pulses energies on the order of 10 μJ at a central wavelength of 2,060 nm, corresponding to a photon number exceeding 10 14 . By implementing SU(1,1) interferometric configuration, we achieve flexible control over the mode structure, allowing the transition between multimode entangled photon pairs and nearly single-mode squeezed states. This results provide a high-intensity quantum light source that facilitates the study of nonclassical ultrafast dynamics.
Squeezed light is a nonclassical state of electro-magnetic field and has noise suppressed below the standard quantum limit in one quadrature component while increased in the other. One of the important applications of squeezed lights is quantum enhanced sensing such as gravitational wave detector with ultimate resolution. Another important application is continuous variables quantum teleportation which utilizes two mode squeezed lights as an essential resource for quantum entanglement. In these applications the final outcome is limited by squeezing level. So it is important to generate highly squeezed light. Over the past few decades a considerable number of the experiments have been performed to generate highly squeezed lights. One of the successful methods is utilization of a sub-threshold optical parametric oscillator (OPO) which includes a nonlinear optical crystal. In this article we will introduce current development of experimental investigation of continuous-wave highly squeezed light by utilizing the OPO and current topics about applications of squeezed light.
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.