Experiments towards quantum information with trapped Calcium ions (original) (raw)

Ground state cooling, quantum state engineering and study of decoherence of ions in Paul traps

Journal of Modern Optics, 2000

We investigate single ions of 40Ca+^{40}Ca^+40Ca+ in Paul traps for quantum information processing. Superpositions of the S$_{1/2}$ electronic ground state and the metastable D$_{5/2}$ state are used to implement a qubit. Laser light on the S$_{1/2} \leftrightarrow$ D$_{5/2}$ transition is used for the manipulation of the ion's quantum state. We apply sideband cooling to the ion and reach the ground state of vibration with up to 99.9% probability. Starting from this Fock state ∣n=0>|n=0>∣n=0>, we demonstrate coherent quantum state manipulation. A large number of Rabi oscillations and a ms-coherence time is observed. Motional heating is measured to be as low as one vibrational quantum in 190 ms. We also report on ground state cooling of two ions.

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

Physical Review Letters, 2009

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.

Tutorial review Cold trapped ions as quantum information processors

In this tutorial we review the physical implementation of quantum computing using a system of cold trapped ions. We discuss systematically all the aspects for making the implementation possible. Firstly, we go through the loading and con®ning of atomic ions in the linear Paul trap, then we describe the collective vibrational motion of trapped ions. Further, we discuss interactions of the ions with a laser beam. We treat the interactions in the travellingwave and standing-wave con®guration for dipole and quadrupole transitions. We review di erent types of laser cooling techniques associated with trapped ions. We address Doppler cooling, sideband cooling in and beyond the Lamb± Dicke limit, sympathetic cooling and laser cooling using electromagnetically induced transparency. After that we discuss the problem of state detection using the electron shelving method. Then quantum gates are described. We introduce single-qubit rotations, two-qubit controlled-NOT and multi-qubit controlled-NOT gates. We also comment on more advanced multiple-qubit logic gates. We describe how quantum logic networks may be used for the synthesis of arbitrary pure quantum states. Finally, we discuss the speed of quantum gates and we also give some numerical estimations for them. A discussion of dynamics on o -resonance transitions associated with a qualitative estimation of the weak-coupling regime is included in Appendix A and of the Lamb±Dicke regime in Appendix B.

Strings of Ion Crystals in a Linear Trap for Quantum Information Processing

Chinese Physics Letters, 2010

Strings of laser cooled 40 Ca + crystals have been successfully confined in our home-built linear ion trap, and ready for quantum information processing. We find the cloud-crystal phase transition of the trapped ions to be strongly sensitive to the frequencies of the Doppler cooling lasers and to the trapping voltage. The quantum jump of a single ion has been observed by controlling the quadrupole transition of the ion by a weak laser with ultra-narrow bandwidth.

Cold trapped ions as quantum information processors

Journal of Modern Optics, 2002

In this tutorial we review physical implementation of quantum computing using a system of cold trapped ions. We discuss systematically all the aspects for making the implementation possible. Firstly, we go through the loading and confining of atomic ions in the linear Paul trap, then we describe the collective vibrational motion of trapped ions. Further, we discuss interactions of the ions with a laser beam. We treat the interactions in the travelling-wave and standing-wave configuration for dipole and quadrupole transitions. We review different types of laser cooling techniques associated with trapped ions. We address Doppler cooling, sideband cooling in and beyond the Lamb-Dicke limit, sympathetic cooling and laser cooling using electromagnetically induced transparency. After that we discuss the problem of state detection using the electron shelving method. Then quantum gates are described. We introduce single-qubit rotations, two-qubit controlled-NOT and multi-qubit controlled-NOT gates. We also comment on more advanced multi-qubit logic gates. We describe how quantum logic networks may be used for the synthesis of arbitrary pure quantum states. Finally, we discuss the speed of quantum gates and we also give some numerical estimations for them. A discussion of dynamics on off-resonant transitions associated with a qualitative estimation of the weak coupling regime and of the Lamb-Dicke regime is included in Appendix.

Quantum information processing and cavity QED experiments with trapped Ca ions

2003

Single trapped Ca+ ions, stored in a linear Paul trap and laser-cooled to the ground state of their harmonic quantum motion are used for quantum information processing. As a demonstration, composite laser pulse sequences were used to implement phase gate and CNOT gate operation. For this, Stark shifts on the qubit transitions were precisely measured and compensated. With a single ion stored inside a high-finesse optical cavity, a cavity mode can be coherently coupled to the qubit transition.

Quantum State Engineering on an Optical Transition and Decoherence in a Paul Trap

Physical Review Letters, 1999

A single Ca+ ion in a Paul trap has been cooled to the ground state of vibration with up to 99.9% probability. Starting from this Fock state |n=0> we have demonstrated coherent quantum state manipulation on an optical transition. Up to 30 Rabi oscillations within 1.4 ms have been observed. We find a similar number of Rabi oscillations after preparation of the ion in the |n=1> Fock state. The coherence of optical state manipulation is only limited by laser and ambient magnetic field fluctuations. Motional heating has been measured to be as low as one vibrational quantum in 190 ms.

Coherent states for trapped ions. Applications in quantum optics and precision measurements

Proc. of the Ninth Meeting on CPT and Lorentz Symmetry (CPT’22), Editor: R. Lehnert, World Scientific, 2023

The evolution of squeezed coherent states of motion for trapped ions is investigated by applying the time-dependent variational principle for the Schrödinger equation. The method is applied in case of Paul and combined traps, for which the classical Hamiltonian and equations of motion are derived. Hence, coherent states provide a natural framework to: (a) engineer quantum correlated states for trapped ions intended for ultraprecise measurements, (b) explore the mechanisms responsible for decoherence, and (c) investigate the quantum–classical transition.

Erratum: Ion-trap Quantum Logic Using Long-Wavelength Radiation

Physical Review Letters - PHYS REV LETT, 2003

A quantum information processor is proposed that combines experimental techniques and technology successfully demonstrated either in nuclear magnetic resonance experiments or with trapped ions. An additional inhomogenenous magnetic field applied to an ion trap i) shifts individual ionic resonances (qubits), making them distinguishable by frequency, and, ii) mediates the coupling between internal and external degrees of freedom of trapped ions. This scheme permits one to individually address and coherently manipulate ions confined in an electrodynamic trap using radiation in the radiofrequency or microwave regime. 03.67.Lx, 42.50.Vk Quantum information processing (QIP) holds the promise of extending today's computing capabilities to problems that, with increasing complexity, require exponentially growing resources in time and/or the number of physical elements . The computation of properties of quantum systems themselves is particularly suited to be performed on a quantum computer, even on a device where logic operations can only be carried out with limited precision . Elements of quantum logic operations have been successfully demonstrated in experiments using ion traps , cavity quantum electrodynamics and in the case of nuclear magnetic resonance (NMR) even algorithms have been performed . Whereas quantum computation with nuclear spins in macroscopic ensembles can most likely not be extended beyond about 10 qubits (quantum mechanical two-state systems) [8], ion traps do not suffer from limited scalability in principle and represent a promising system to explore QIP experimentally. They can be employed to also investigate fundamental questions of quantum physics, for example related to decoherence [9] or multiparticle entanglement . However, they still pose considerable experimental challenges.