Individual Addressing of Trapped Ions and Coupling of Motional and Spin States Using rf Radiation

Abstract

Individual electrodynamically trapped and laser cooled ions are addressed in frequency space using radio-frequency radiation in the presence of a static magnetic field gradient. In addition, an interaction between motional and spin states induced by an rf field is demonstrated employing rfoptical double resonance spectroscopy. These are two essential experimental steps towards realizing a novel concept for implementing quantum simulations and quantum computing with trapped ions.PACS numbers: 37.10. Vz, 37.10.Ty, 32.60.+i Quantum simulations addressing a specific scientific problem and universal quantum computation are expected to yield new insight into as of yet unsolved physical problems that withstand efficient treatment on a classical computer (e.g., [1]). Already a small number of qubits (i.e., a few tens) used for quantum simulations could solve problems even beyond the realm of quantum information science. Creating and investigating entanglement in large physical systems is a related important experimental challenge with implications for our understanding of the transition between the elusive quantum regime and the classical world [2].Laser cooled atomic ions confined in an electrodynamic cage have successfully been used for quantum information processing (QIP) [3] and advantages and difficulties associated with this system have been and still are subject to detailed investigations. The electromagnetic radiation used to coherently drive ionic resonances that serve as qubits needs to be stable against variations in frequency, phase, and amplitude over the course of a quantum computation or simulation. Experimentally this is particularly challenging when laser light is used for realizing quantum gates. When employing laser light additional issues need to be dealt with to allow for accurate qubit manipulation such as the intensity profile of the laser beam, its pointing stability, and diffraction effects. Furthermore, the motional state of the ion chain strongly affects the gate fidelity which requires ground state cooling and low heating rates during the gate operation [4]. Also, spontaneous scattering of laser light off excited electronic states may pose a limit for the coherence time of a quantum many-body state. The probability for scattering can be reduced by increasing the detuning from excited states (when two laser light fields are used that drive a Raman transition between hyperfine or Zeeman states) which, however, leads to an increasing demand for laser power [5].For generating Raman laser beams with a desired frequency difference, first a radio-frequency (rf) or microwave signal at this difference frequency has to be generated that is then "imprinted" on the laser light and send to the ions. Using rf or microwave radiation directly for coherent driving of qubit transitions is impeded in usual ion trap schemes, since, (i) individual addressing of qubits by focusing radiation on just one ion is difficult due to the long wavelength of rf radiation, and (ii) the required coupling between qubit stat...

The trapped-ion qubit tool box

“…It is important to note that our review is not at all exhaustive. For example, in the last few years, alternative methods have been suggested, with a few initial demonstrations, in which a universal quantum gate set is performed on trapped-ion qubits using only microwave fields [51][52][53][54][55]. Here, momentum transfer to trapped-ions is achieved with strong magnetic field gradients.…”

“…The qubit levels are coupled by electro-magnetic (e.m.) traveling plane waves, i.e., we assume that the ion is placed in the far-field of the e.m. radiation. This assumption does not always hold, however, and there have been several proposals to implement ion qubit gates using near-field e.m. fields [3,[51][52][53][54][55]. The qubit evolution is determined by the time dependent Hamiltonian,…”

Temperature-independent quantum logic for molecular spectroscopy

“…In order to discriminate Zeeman states within a molecular rovibrational level, we develop a second version of the protocol, based on the use of magnetic forces, which result from the coupling of a magnetic field gradient with the effective magnetic moment µ of the particle [23,24],…”

Finite-temperature crossover from a crystalline to a cluster phase for a confined finite chain of ions

“…This is in particular due to the application of the dynamics of ionic systems to spectroscopy [1,2], the implementation of quantum simulations [3,4], and the realization of quantum information processors [5,6]. In this context many trapping methods [7][8][9][10][11] have been suggested.…”