Quantum technology relies on the behaviour of quantum superposition states. It is generally desirable to work with longlived superpositions as these give the greatest benefit. For example, when measuring forces, accelerations, magnetic and electric fields, or just the passage of time, long-lived superpositions give the highest sensitivity and that is the key advantage of quantum sensing. For computation, long coherence time increases the available computing power. The most convenient way to manipulate the internal quantum states of an atom (or ion or molecule) is using laser light that couples to the charge distortion of the atom. Two stable, low-lying atomic states can be superposed using a pair of laser beams whose frequencies differ by the microwave frequency linking the two states. This is called a Raman transition. The microwave beat note between the two laser frequencies is transferred to the quantum superposition of atomic states, which then oscillates at the microwave frequency, with the phase impressed by the lasers. To make the most of quantum interference, one needs lasers of stable intensity -- preferably high intensity -- and exceptionally low phase noise in the beat note. For many such applications, no suitable laser system is commercially available. That is the problem we address here. The SolsTis produced by M-Squared Lasers is a very stable, high-power laser, which provides the ideal starting point
for developing a suitable product. It is broadly-tuneable across the near infrared range (700 nm - 1,000 nm), so it can address a wide range of relevant atoms, particularly the two workhorse atoms rubidium and caesium.
The team at Imperial College is developing accelerometers for inertial navigation using atomic quantum coherence in rubidium atoms. This application is challenging as the lasers driving the Raman transition must combine high power, exceptionally low phase noise, low drift, and great agility of power, frequency and phase. We propose to work closely with M-Squared to develop a packaged laser system that optimises the performance of these accelerometers. This involves research to define the optimum specifications and development to deliver those specifications in a commercial package. The goal of the present proposal is to define and then produce a suitable laser system, and to validate it by demonstrating high performance, first in a 1-axis accelerometer and then in a 3-axis prototype.
The system will be developed and validated in the context of a new method for navigating without recourse to the satellite network, which has military and transport applications. However, it will be much more widely useful because of the general importance of Raman transitions in quantum technology. Other probable applications include geological surveying, mining, ultra-precise time stamping, medical imaging, and quantum information processing.
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