Spatially multimode squeezed light for quantum imaging and one-way quantum computing

When recorded with sensitive detectors, the electric field of the light reveals unavoidable quantum fluctuations in its phase and amplitude. It is a manifestation of the Heisenberg uncertainty principle. While it is impossible to create a light field with simultaneously known phase and amplitude, it is possible to reduce the quantum noise of either the phase or the amplitude in exchange of increased quantum noise on the other variable. This phenomenon is known as squeezing.Up till now, strongly squeezed light has only been produced in one single optical mode at a time (typically a Gaussian beam). This means that the fluctuations of the beam are squeezed when the field is considered in its full spatial extent but that measuring only a portion of the cross-section of the beam will yield little squeezing. For instance, an amplitude-squeezed beam will have reduced fluctuations in its total power, but its intensity profile will still present some roughness (local fluctuations). This proposal aims to produce light fields that are squeezed in amplitude at any point of their transverse profile. As a consequence, the intensity profile should be smooth, even at the quantum level. From a different point of view, the beam is squeezed in multiple transverse optical modes, hence the name multi-spatial-mode (MSM) squeezed light .The starting point will be four-wave mixing in an atomic vapour, a non-linear process in which the medium, when pumped by an intense laser beam, converts a pair of incoming photons into two photons with correlated positions and directions. The output of the four-wave mixing process contains strong correlations at the photon level and can be further transformed through simple linear optics into a MSM squeezed beam of light, where the photons are regularly distributed inside the beam.We will apply this non-classical state of light to two experiment which epitomise two aspects of modern quantum optics: quantum measurements and quantum information processing.First, we will show that MSM squeezed light can improve the quantum limit on optical resolution. In a microscopy set-up, MSM squeezed illumination of the observed object allows for the formation of a smoother image, with reduced spatial quantum noise. Using known techniques of super-resolution, it is then possible to reconstruct the objects in greater details than what would be possible with classical illumination.Second, we will demonstrate the potential of MSM squeezed light to produce quantum states of light that are relevant to a class of quantum computing. These states, called cluster states, are made of a collection of entangled modes and can be built from an ensemble of squeezed beams with a network of beam-splitters. Since MSM squeezed light corresponds to a collection of squeezed optical modes, it actually constitutes the proper resource for the creation of a cluster state. As a demonstration, we will seek to produce a small cluster state.

The proposed research is fundamental in nature. It is part of a sustained global effort to turn quantum mechanics into useful technology. The economic and social impact of quantum information science will be apparent on a longer timescale, probably more than 10 years, but it will potentially be very important. Quantum technologies hold the promise of increased computational power, with potential applications ranging from simulation of superconducting materials to drug design, as well as absolutely secure communications. The two parts of the project, the quantum computation part and the quantum imaging part, are likely to have different types of impact. Quantum computation: Since quantum information science is still at an early stage of development, one of the best ways to guarantee the impact of the proposed research will be to maximise its exposure to the scientific community working in the field. This will be done using the usual conduits of scientific results such as publications in appropriate journals and presentations at national and international conferences, theoretically oriented (TQC in the UK) as well as more applied (CLEO/QELS in the USA). We will also keep our web page on the Midland Ultracold Atom Research Centre website up to date, and report the latest important results on the front page. It is worth noting that we are engaged in an international effort (EU project iSense) to create practical quantum devices for precision sensing and also, in a longer term, for quantum storage. One of our partners is QinetiQ, who has extensive experience in turning science into applications. This gives us the resources, the connections and the infrastructure to bring any scientific breakthrough closer to practical applications if the opportunity occurs. Quantum imaging: The quantum imaging part of the project is likely to generate interest more quickly, because the need for better optical resolution is universal. We will study the possibility of developing the technique for applications that we know are almost ripe for benefiting from the research, such as motion tracking inside optical tweezers. For the other possible applications that we are not aware of, we will rely on our collaborators: QinetiQ with their experience in bringing science to the market and Prof. Kolobov, who has been advising the industry on this particular topic for years. Finally, an important potential user of this research is the general public, who is often eager to learn about the latest quantum feats. To this effect, we will create an outreach section on the MUARC website where we will make our research accessible to the public in simple terms. We will also advertise our best results by way of press releases and on the front page of our website.