Ion Trapping QIP
Trapped ions are arguably the physical system that has advanced the most in experimental quantum information research. Perhaps the biggest challenge for trapped ions is to demonstrate progress towards a scaleable system. Alongside that is a drive to use ion-photon entanglement to transmit quantum information between remote ion traps. A popular review article gives an insight into current achievements and status of this research field.
In the past, most ion trap experiments have been performed using traps of bulk metallic electrodes. While this has been successful for several important quantum information and entanglement experiments, there is now an international drive to create microfabricated ion traps which have the possibility of being scaled up to contain many arrays of ions in a single chip.
Microfabricated ion traps made of alumina, where the electrodes are laser-machined and gold-coated, were the first type of 'microtraps' to become operational. Wineland's group at NIST Boulder used this type of trap to perform successful experiments such as quantum teleportation, amongst others. Monroe's group at Michigan (NB: Chris Monroe is now at Maryland), were the first group to demonstrate ion transport around a 90-degree corner, and achieved this using a gold-coated alumina trap. The first monolithic microfabricated trap was a structure based on GaAs and is the first step towards using existing sophisticated device fabrication technology.
Lithographic and etching techniques are required for creating trap chips with larger number of electrodes, and subsequently larger arrays of trapped ions. NPL has proposed a design for a monolithic microfabricated ion trap chip; this is based on silica-on-silicon technology more commonly found in the photonics industry. The concept is illustrated in the figure below.
This is an ambitious structure, and is currently being developed. Most of the processing steps used to create the structure have been demonstrated; efforts are now concentrated on combining these steps to create a simple structure such as the one shown above. With this activity, NPL is participating in an EU project entitled 'Microtrap'; the aim is for European ion trap groups to build capability in microfabricated ion traps.
With a functioning trap, our aim is to trap small strings of ions and investigate schemes for ion-ion entanglement. Beyond this there are intriguing opportunities for using entangled ions to enhance precision measurement schemes. The experimental side of this subject is relatively young; Demonstrations of Heisenberg-limited spectroscopy and other techniques for precision spectroscopy have all used entangled trapped ions.
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