Ion trap in a chip


The Geonium Chip, is a novel ion trap technology  with pioneering applications in quantum technology and mass spectrometry. The chip’s main element is the Coplanar-Waveguide Penning trap (CPW-trap).  This is a surface ion (Pe
nning) trap conceived and developed at Sussex. Figure 1 shows a sketch of the Geonium Chip. Any charged particles, such as electrons, protons, atomic nuclei, molecular ions, clusters, etc. can be captured and stored for long times at some distance of above the surface of the chip.


Geonium Chip Drawing

Figure 1. Sketch of the Geonium chip.

The CPW-trap in the chip consists of five rectangular electrodes and a static magnetic field, as shown in Figure 1. The trap’s working principle is straightforward. The magnetic field, B=B uz, forces the charged particle to follow a closed (cyclotron) orbit around the uz axis, hence trapping it “radially”, along the x and y axes. Static voltages applied to the electrodes generate a harmonic potential well, confining the particle “axially”, along the z axis. The particle’s confined trajectory is shown in Figure 2. It is the superposition of three oscillators: the “cyclotron” and “axial” motions, with frequencies ωp and ωz, respectively, and the slow “magnetron” drift, with frequency ωm.


Figure 2. Motion of a trapped particle.

Geonium Atoms

Cryogenic Penning traps permit a very accurate control of the dynamics of a trapped electron, at the level of inducing and observing quantum jumps between its Fock-states. The rest gas pressure in cryogenic vacuum chambers amounts to 10-16 mbar or lower, allowing for a very prolonged capture of the particles. These are confined for months, cooled down to the ground state and observed non-destructively. Moreover, the continuous Stern-Gerlach effect permits the detection and manipulation of the electron’s spin, while the Purcell effect enhances the coherence time of its quantum state. Hence, cryogenic Penning traps are excellent quantum laboratories.

GeoniumChip 1st generation

Figure 3. First generation Geonium Chip. Microfabricated with a thin layer of gold (700 nm) on a silicon substrate.

A single electron captured in a Penning trap is also known as a geonium atom, as coined by the Nobel Prize laureate Hans Dehmelt. It is an outstanding system for testing the laws of physics with ultra high precision. An example is the measurement of electron’s intrinsic magnetic dipole moment, achieved with a relative uncertainty of 10-13. That and other advanced Penning trap experiments, invariably employ a very large superconducting solenoid. Our research goals radically change that concept: we are integrating the trap and the magnetic filed source in a single chip of a few cm2: the Geonium Chip.

1st generation chip sketch

Figure 4. Trap’s electrodes. The electrodes originate from the 3D cylindrical trap.


Building blocks of quantum microwave circuits 

Incorporating different quantum systems in a common “motherboard” and interfacing them through a shared quantum bus is an essential requirement of any prospective quantum technology. The Geonium Chip satisfies this demand. Its design as a Coplanar-Waveguide (CPW) transmission-line is planned for its direct integration within  quantum microwave circuits.

Trapped electrons can be coupled to microwave photons, via interaction with the cyclotron motion or with the spin. This renders possible their coherent interaction with other quantum systems, enabling the exchange of quantum information. The Geonium Chip is conceived as a building block of future quantum microwave circuits, where increasing numbers of CPW-traps, superconducting microwave cavities, solid-state quantum devices and other types of ion or neutral atom traps might be coherently coupled through microwave photons.


Quantum Circuit

Figure 5. Coupling a trapped electron to a quantum microwave circuit.

Coherent Coupling

Figure 6. Exchange of quantum information between the electron and the microwave cavity.