Quantum computers are regarded as the technology of the future when it comes to powerful computing systems. Various technological approaches currently exist to realize such systems, including superconducting circuits, photonic circuits or individual atomic qubits, such as neutral atoms and trapped ions. Neutral atoms in optical tweezers in particular are a comparatively young field of research, but are making rapid progress compared to other technologies. In the project “Scalable Optical Modulators for Atomic Quantum Computers”, SMAQ for short, which was realized as part of the QNC Space of the Research Fab Microelectronics Germany (FMD), the Fraunhofer IPMS and the Max Planck Institute of Quantum Optics have now achieved significant successes in the development of neutral atom and atom trap quantum computers.
Lasers as quantum exciters
Quantum computers based on charged or neutral atomic qubits offer a number of advantages over alternative technologies. They enable an intrinsically high quality of the individual qubits, i.e. the charge carriers of the computing system, and thus achieve excellent coherence times and gate qualities. In order for neutral atoms to become qubits, their quantum states must be addressed with high-precision lasers. Strontium atoms are used in atomic quantum computers to generate qubits. These atoms are manipulated in the UV range, as important electronic transitions that can be used to excite their quantum states can only be achieved in the ultraviolet spectral range. The Max Planck Institute of Quantum Optics has been researching the arrangement and addressing of neutral atoms for some time. The hardware for the spatial modulation of the required UV rays is currently in the development phase. There is currently a lack of scalable and sufficiently precise solutions that can be used to excite qubits individually. In the project, it has now been demonstrated that spatial light modulators (SLMs) based on perpendicular mirror arrays can be used to realize optical point gratings of high quality in the relevant UV wavelength range.
Fraunhofer IPMS has special expertise in such perpendicular mirror arrays. The strontium atoms used for qubit generation are cooled by laser cooling in the experiment, led by the Max Planck Institute of Quantum Optics, and captured in optical point gratings. In the joint project, the complementary expertise of both partners was brought together to advance into new regimes in atomic quantum computing. To this end, Fraunhofer IPMS further developed a micromirror-based area light modulator that can be used to generate programmable and high-precision patterns (in the nm range). The generated phase patterns can then be converted into any laser beam pattern using the appropriate optics. As part of the project, a corresponding element was made available to the Max Planck Institute of Quantum Optics for testing and its performance was demonstrated in all areas.
In future work, the tiny atoms can be captured in the focal points of the laser beams and held in specific positions. The laser beams then function as so-called “optical tweezers”. Their internal quantum states are then manipulated with precise pulses to perform quantum logic operations for quantum computation.
Dr. Michael Wagner from Fraunhofer IPMS says of the successful project: “Our SLM systems enable light modulation down to the deep UV range.
Micromirror technology offers a number of advantages over liquid crystal-based light modulators, such as UV suitability, higher modulation speeds down to the megahertz range and polarization-independent work.” In addition to proving the suitability of SLM for quantum optical experiments in the UV range by the Fraunhofer IPMS and the successful qualification for the experimental set-up by the Max Planck Institute, the focus of the project was on evaluating the accuracy of the phase modulation. Phase control in the range of well below one hundredth of a wavelength was demonstrated and thus meets the highest requirements for the quality of optical tweezers.
The next step on the way to quantum systems
The use of micromirror-based area light modulators for pattern generation and qubit control opens up a new dimension in terms of precision and scalability. The demonstrator developed and the project results are key parameters for the targeted further development of SLM technology for applications in the quantum range. They can provide a reliable basis for the realization of an addressing device in the future. One of the next goals is to develop SLMs that enable the parallel generation of several 1,000 focused laser beams in the ultraviolet spectral range. The focus is also on increasing the system speed. The 1 kHz currently realized only represents a starting value for significantly faster modulators in the future.
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Further links
👉 www.ipms.fraunhofer.de
Photo: Fraunhofer IPMS
