Research reports: Technologies for Quantum Computing

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Quantum hardware

Below you will find interesting facts and research reports about our latest developments in quantum computing:

Our technology for a step into the future: 

Addressing optics for ion and atom trap based quantum computers.

Realization of a scalable quantum computer

In the project "Advanced quantum computing with trapped ions" (AQTION), a component of the quantum flagship program of the EU, a scalable ion trap-based quantum computer was realized. This was being built and deployed at the University of Innsbruck, the consortium leader of the AQTION network.

In the long term, great things are planned within the framework of the AQTION alliance: The goal of the project partners is to build a powerful quantum computer suitable for industrial use and to significantly advance applied research on quantum computing in Germany.

Ion-based quantum computer

The quantum computer developed in the AQTION research project is based on so-called "ion QuBits". The system uses stored ions as QuBits, which can be held in electromagnetic traps and controlled within them with laser beams. For this purpose, a laser-optical setup was realized at Fraunhofer IOF, which enables the manipulation of ions in the ion trap for quantum computers.

Manipulate and measure the state of the ions

Within the AQTION quantum computer, the quantum bits (Qbits) are represented by Ca⁺-ions, which are confined within a Paul trap. In order to prepare the quantum states and execute calculations at the quantum gate, different laser wavelengths are used. This includes to illuminate single ions with a laser spot of a wavelength of 729 nm (Fig. 3). The result of the calculations is "read out" from the status of the ions that are arranged in a linear chain within the trap. The status of the ion at the time of the measurement becomes apparent by checking whether a fluorescence signal is emitted or not.

Accurate addressing of the ions

Reliable addressing of the ions that are spaced by 3 microns approximately in the center of the trap requires diffraction-limited spots, on one hand, and on the other a means of tracking the spots along the trap axis with sub-micron accuracy. To this end, a particular optomechanical unit was developed where in a special solid-state-joint configuration piezo-actuators induce a linear movement of micro-prisms, figure 1. The optomechanical unit transforms the fixed array of input-fibers in a dynamically adjustable arrangement of sources. The additional optics ensure the demagnification of the source distances at the input down to the ion distances, as well as the appropriate spot sizes in the plane of the trap. In addition to a special objective, which is corrected for the wavelengths of the addressing beam and the fluorescence detection, gradient index and achromatic lenses are used.  

Miniaturization of the system

For the overall optical setup (Fig. 3), a multiple folding of the beam path (Fig. 1 (left) and Fig. 2) is required to ensure the potential for integration. To have the optimum focal length of the parabolic mirror – an essential component for the device principle (submitted as patent application) – this mirror is constructed by ultra-precision machining at Fraunhofer IOF.

Authors

Bernd Höfer, Felix Kraze, Peter Schreiber, Christoph Wächter, Uwe Zeitner

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