Our group is working towards quantum information processing using trapped ions. The calcium ions we use are calcium atoms from each of which with one outermost electron is removed. Because they are positively charged, they can be strongly controlled when an external electric field is applied. This property can be used to trap ions in a “container” called an ion trap. When the ions are trapped, they are initially in a state of intense thermal motion, but we can use laser beams to remove heat (laser cooling), then the ions can be kept almost completely still in space (see below).
In this state, the ions (atoms) are almost completely unaffected by their own thermal motion or by surrounding disturbances, and each of those ions can be observed individually; this is a special situation. In other words, we are in a situation where we have direct access to things in the microscopic world. At this time, quantum nature, which is a property of objects in the microscopic world, becomes apparent.
For example, a phenomenon called “quantum jumps” has been observed. The electronss in an ion can only take discrete energy at specific levels due to their quantum nature. The energy of the outermost electron in an ion can be changed by light from outside. For trapped ions, experiments have captured the moment when this change occurs. (see below).
In recent years, quantum computation, which achieves dramatically higher computational performance than conventional computers, and quantum simulations, which attempt to simulate the behavior of complex physical systems that are difficult to be predicted with convenrional computation with other, more controllable physical systems, have been proposed and actively studied. The above characteristics of trapped ions can be used for such applications.