Diffractive beam splitters quantum applications

Quantum technologies are an emerging field of interest in the computing and communication industries, with many exciting commercial possibilities. Nevertheless, Quantum technologies face many challenges in commercialization, with one of the major ones being scaling of quantum systems to useful scales. Holo/Or diffractive beam splitter elements find increasing use in efforts to scale up optics-based quantum computing systems. Diffractive beam splitter quantum applications cover a wide range of use cases, from generating an array of bright spots to trap atoms, through multiplexing signals coming from waveguide quantum computer chips to simultaneous excitation of quantum dot arrays.  In this article we review Diffractive beam splitter operating principles, their advantages for quantum technologies, and some typical quantum optical applications that use diffractive beam splitters.

Diffractive Beam splitters theory

Diffractive beam splitters flat, transmissive optical elements that split an incoming laser beam into multiple beams with pre-determined power ratios and separation angles. The simplest and best-known type of diffractive beam splitters are binary gratings, which send the light into two main orders. In a similar manner, beamsplitter matrix elements, a 2D version of the diffraction grating, generate 2D arrays of spots with equal separations and uniform intensity. They do this by having periodic structures on their surface that generate a phase delay of the laser light going through different areas of the DOE. This creates a phase profile that causes diffraction into multiple orders, each having its own angle. If focused by a lens, each order generates a spot at a fixed separation relative to the other orders.

Requirements and constraints of using diffractive beam splitters in quantum applications

Diffractive Beam splitters are robust elements that are insensitive to tolerances including positioning, small tilts 9up to 5 deg), or input beam size. Nevertheless, integrating a diffractive beam splitter in quantum laser applications does require several considerations: • Narrow bandwidth- Like all DOEs, diffractive beam splitters are designed for a nominal wavelength, and operate within spec only in band of +-2% of this wavelength.

• Field correction- The focus optics used must compensate for the field distortion at higher splitting angles. This is mostly relevant when working with large fields and high NA.

Beam splitter quantum technologies applications

Diffractive Beam splitters find many applications in laser quantum technologies. These include:

• Generating arrays of optical traps, i.e optical tweezer arrays. In some quantum computing approaches, the qubit are isolated ultracold atoms, that must be carefully held in place using laser tweezers, i.e optical forces generated by focused laser spots . To generate large arrays of such atoms, with precise separation required for controlled interaction, multi spot 2D beam splitter DOEs are often used.
• Parallel readout of multiple solid state qubits using a diffractive beam splitter. In approaches utilizing solid state color center spin qubits, the qubit state is often sampled using optically detected magnetic resonance (ODMR), requiring excitation of the qubit with a tight laser spot. Using a 2D diffractive beam splitter matrix, multiple Qubit can be selectively samples without altering the state of others, over large arrays of qubit.
• Planar Lightwave technology is another promising approach to quantum computation. In this approach, Qubits are represented as weakly coupled modes in planar waveguides, and the computation is done optically by coupling light into the waveguide and coupling the answers out of the waveguide. Diffractive bam splitter elements are useful to couple specific modes from a certain waveguide to a different waveguide on another chip, through a free-space interface.

Conclusion

Diffractive beam splitters are flat, thin optical elements that can generate an array of output beams from an input laser beam, with precise separations and pre-designed power ratios. These diffractive elements are highly useful in quantum technologies in a variety of applications. Bam splitter quantum applications include generation of optical traps arrays, simultaneous excitation of several quantum-dot Qubits, and multiplexing signals coming from waveguide-based quantum computers.