Abstract
Broadband multimode squeezers constitute a powerful quantum resource with promising potential for different applications in quantum information technologies such as information coding in quantum communication networks or quantum simulations in higher-dimensional systems. However, the characterization of a large array of squeezers that coexist in a single spatial mode is challenging. In this paper, we address this problem and propose a straightforward method for determining the number of squeezers and their respective squeezing strengths by using broadband multimode correlation function measurements. These measurements employ the large detection windows of the state of the art avalanche photodiodes in order to simultaneously probe the full Hilbert space of the generated state, which enables us to benchmark the squeezed states. Moreover, due to the structure of correlation functions, our measurements are not affected by losses. This is a significant advantage, since detectors with low efficiencies are sufficient. Our approach is less costly than tomographic methods relying on multimode homodyne detection, which is based on much more demanding measurement and analysis tools and appear to be impractical for large Hilbert spaces.
Highlights
The study of correlation functions has a long history and lies at the heart of coherence theory [1]
In this paper we address this problem and propose a straightforward method to determine the number of squeezers and their respective squeezing strengths by using broadband multimode correlation function measurements
Since correlation functions have become an standard tool in quantum optical experiments to study the properties of laser beams [3], parametric downconversion sources[4, 5] or heralded single-photons [6, 7, 8]
Summary
The study of correlation functions has a long history and lies at the heart of coherence theory [1]. Our scheme of measuring broadband multimode correlation functions of pulsed quantum light is especially useful for probing squeezed states These states are commonly generated via the interaction of light with a crystal exhibiting a χ(2)-nonlinearity, a process referred to as parametric downconversion (PDC)[12, 13, 14, 15, 16, 17] or with optical fibers featuring a χ(3)-nonlinearity called four-wave-mixing (FWM) [18, 19]. In general the generated squeezed states exhibit multimode characteristics in the spectral degree of freedom, i.e. a set of independent squeezed states is created with each squeezer residing in its own Hilbert space This inherent multimode character renders these states powerful for coding quantum information, yet the same feature impedes a proper experimental characterization in a straightforward manner.
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