The development of the quantum information research field opens a number of new opportunities in the information technology area. This includes data processing possibilities unique for the quantum world leading to new computation algorithms, safe methods for the transmission of coded messages and teleportation of information.
There is intensive worldwide work to develop hardware by which the new concepts can be demonstrated and implemented. In Lund we develop hardware for quantum computers based on rare-earth-ion doped inorganic crystals and we are also working on a quantum memory concept for quantum repeaters that can be used for long distance quantum cryptography.
One of our crystals (Pr doped Y2SiO5)
In addition of being used for quantum information tasks, the development of quantum hardware may be equally important for the general development of micro- and nano-technology. Decreasing dimensions makes it increasingly important to fully control the quantum mechanical properties of systems and materials employed and the development of quantum computer hardware is a systematic approach for learning how to control and how to develop controllable quantum systems. Thus quantum hardware development is expected to have decisive influence of the development of the micro-electronics and nano-technology areas.
A material suitable as quantum computer hardware generally should have a large number of two-level quantum systems which can act as quantum bits. There are a number of particularly important properties that these two-level systems (qubits) should fulfil.
- They should have long coherence times and it should be possible to control them independent of each other. Control here means the ability to prepare any of these two-level systems in an arbitrary superposition state with a definite phase.
- It should be possible for the qubits to control each other in order to carry out two-bit gate operations and logics.
- It should be possible to read the value of the qubits.
In our case the qubit levels are two different hyperfine states in the rare earth ion ground states which have very long coherence time. The last two years we have devoted considerable time to construct a laser system with sufficient frequency and phase stability to control our rare-earth-ion wave functions with the precision needed for the quantum state manipulations (see picture below) and we are now using this for qubit manipulations and in our quantum memory development work.
The figure shows an overview of the laser stabilisation system. As far as we know it is by far the most frequency-stable laser system in Europe presently operating at 606 nm.