Ion trap

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Ion trap, shown here is one used for experiments towards realizing a quantum computer. Ionenfalle - Quantencomputer.jpg
Ion trap, shown here is one used for experiments towards realizing a quantum computer.

An ion trap is a combination of electric or magnetic fields used to capture charged particles — known as ions — often in a system isolated from an external environment. Ion traps have a number of scientific uses such as mass spectrometry, basic physics research, and controlling quantum states. The two most common types of ion trap are the Penning trap, which forms a potential via a combination of electric and magnetic fields, and the Paul trap which forms a potential via a combination of static and oscillating electric fields.

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Penning traps can be used for precise magnetic measurements in spectroscopy. Studies of quantum state manipulation most often use the Paul trap. This may lead to a trapped ion quantum computer [1] and has already been used to create the world's most accurate atomic clocks. [2] [3] Electron guns (a device emitting high-speed electrons, used in CRTs) can use an ion trap to prevent degradation of the cathode by positive ions.

Ion trap mass spectrometers

A linear ion trap component of a mass spectrometer. Dual linear ion trap.JPG
A linear ion trap component of a mass spectrometer.

An ion trap mass spectrometer may incorporate a Penning trap (Fourier transform ion cyclotron resonance), [4] Paul trap [5] or the Kingdon trap. [6] The Orbitrap, introduced in 2005, is based on the Kingdon trap. [7] Other types of mass spectrometers may also use a linear quadrupole ion trap as a selective mass filter.

Penning ion trap

FTICR mass spectrometer - an example of a Penning trap instrument. IonSpec FT-ICR (Fourier transform Ion cyclotron resonance) Mass spectrometer.jpg
FTICR mass spectrometer - an example of a Penning trap instrument.

A Penning trap stores charged particles using a strong homogeneous axial magnetic field to confine particles radially and a quadrupole electric field to confine the particles axially. [8] Penning traps are well suited for measurements of the properties of ions and stable charged subatomic particles. Precision studies of the electron magnetic moment by Dehmelt and others are an important topic in modern physics.

Penning traps can be used in quantum computation and quantum information processing [9] and are used at CERN to store antimatter. Penning traps form the basis of Fourier transform ion cyclotron resonance mass spectrometry for determining the mass-to-charge ratio of ions. [10]

The Penning Trap was invented by Frans Michel Penning and Hans Georg Dehmelt, who built the first trap in the 1950s. [11]

Paul ion trap

Schematic diagram of ion trap mass spectrometer with an electrospray ionization (ESI) source and Paul ion trap. Bruker HCT-schematicJune2008.PNG
Schematic diagram of ion trap mass spectrometer with an electrospray ionization (ESI) source and Paul ion trap.

A Paul trap is a type of quadrupole ion trap that uses static direct current (DC) and radio frequency (RF) oscillating electric fields to trap ions. Paul traps are commonly used as components of a mass spectrometer. The invention of the 3D quadrupole ion trap itself is attributed to Wolfgang Paul who shared the Nobel Prize in Physics in 1989 for this work. [12] [13] The trap consists of two hyperbolic metal electrodes with their foci facing each other and a hyperbolic ring electrode halfway between the other two electrodes. Ions are trapped in the space between these three electrodes by the oscillating and static electric fields.

Kingdon trap and orbitrap

Partial cross-section of Orbitrap mass analyzer - an example of a Kingdon trap. Orbitrap mass analyzer - partial cross-section.JPG
Partial cross-section of Orbitrap mass analyzer - an example of a Kingdon trap.

A Kingdon trap consists of a thin central wire, an outer cylindrical electrode and isolated end cap electrodes at both ends. A static applied voltage results in a radial logarithmic potential between the electrodes. [14] In a Kingdon trap there is no potential minimum to store the ions; however, they are stored with a finite angular momentum about the central wire and the applied electric field in the device allows for the stability of the ion trajectories. [15] In 1981, Knight introduced a modified outer electrode that included an axial quadrupole term that confines the ions on the trap axis. [16] The dynamic Kingdon trap has an additional AC voltage that uses strong defocusing to permanently store charged particles. [17] The dynamic Kingdon trap does not require the trapped ions to have angular momentum with respect to the filament. An Orbitrap is a modified Kingdon trap that is used for mass spectrometry. Though the idea has been suggested and computer simulations performed [18] neither the Kingdon nor the Knight configurations were reported to produce mass spectra, as the simulations indicated mass resolving power would be problematic.

Cathode ray tubes

Ion traps were used in television receivers prior to the introduction of aluminized CRT faces around 1958, to protect the phosphor screen from ions. [19] The ion trap must be delicately adjusted for maximum brightness. [20] [21]

Trapped ion quantum computer

Some experimental work towards developing quantum computers use trapped ions. Units of quantum information called qubits are stored in stable electronic states of each ion, and quantum information can be processed and transferred through the collective quantized motion of the ions, interacting by the Coulomb force. Lasers are applied to induce coupling between the qubit states (for single qubit operations) or between the internal qubit states and external motional states (for entanglement between qubits).

Related Research Articles

Atomic electron transition is a change of an electron from one energy level to another within an atom or artificial atom. It appears discontinuous as the electron "jumps" from one energy level to another, typically in a few nanoseconds or less. It is also known as an electronic (de-)excitation or atomic transition or quantum jump.

Mass spectrometry (MS) is an analytical technique that measures the mass-to-charge ratio of ions. The results are typically presented as a mass spectrum, a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures.

Ion source Device that creates charged atoms and molecules (ions)

An ion source is a device that creates atomic and molecular ions. Ion sources are used to form ions for mass spectrometers, optical emission spectrometers, particle accelerators, ion implanters and ion engines.

Penning trap

A Penning trap is a device for the storage of charged particles using a homogeneous axial magnetic field and an inhomogeneous quadrupole electric field. This kind of trap is particularly well suited to precision measurements of properties of ions and stable subatomic particles. Geonium atoms have been created and studied this way, to measure the electron magnetic moment. Recently these traps have been used in the physical realization of quantum computation and quantum information processing by trapping qubits. Penning traps are used in many laboratories worldwide, including CERN, to store antimatter such as antiprotons.

Wolfgang Paul German physicist

Wolfgang Paul was a German physicist, who co-developed the non-magnetic quadrupole mass filter which laid the foundation for what is now called an ion trap. He shared one-half of the Nobel Prize in Physics in 1989 for this work with Hans Georg Dehmelt; the other half of the Prize in that year was awarded to Norman Foster Ramsey, Jr.

Tandem mass spectrometry

Tandem mass spectrometry, also known as MS/MS or MS2, is a technique in instrumental analysis where two or more mass analyzers are coupled together using an additional reaction step to increase their abilities to analyse chemical samples. A common use of tandem-MS is the analysis of biomolecules, such as proteins and peptides.

Quadrupole mass analyzer

The quadrupole mass analyzer (QMS), also known as a transmission quadrupole mass spectrometer, quadrupole mass filter, or quadrupole mass spectrometer, is one type of mass analyzer used in mass spectrometry. As the name implies, it consists of four cylindrical rods, set parallel to each other. In a quadrupole mass spectrometer the quadrupole is the mass analyzer - the component of the instrument responsible for selecting sample ions based on their mass-to-charge ratio (m/z). Ions are separated in a quadrupole based on the stability of their trajectories in the oscillating electric fields that are applied to the rods.

Trapped ion quantum computer Proposed quantum computer implementation

A trapped ion quantum computer is one proposed approach to a large-scale quantum computer. Ions, or charged atomic particles, can be confined and suspended in free space using electromagnetic fields. Qubits are stored in stable electronic states of each ion, and quantum information can be transferred through the collective quantized motion of the ions in a shared trap. Lasers are applied to induce coupling between the qubit states or coupling between the internal qubit states and the external motional states.

Quadrupole ion trap

A quadrupole ion trap is a type of ion trap that uses dynamic electric fields to trap charged particles. They are also called radio frequency (RF) traps or Paul traps in honor of Wolfgang Paul, who invented the device and shared the Nobel Prize in Physics in 1989 for this work. It is used as a component of a mass spectrometer or a trapped ion quantum computer.

History of mass spectrometry

The history of mass spectrometry has its roots in physical and chemical studies regarding the nature of matter. The study of gas discharges in the mid 19th century led to the discovery of anode and cathode rays, which turned out to be positive ions and electrons. Improved capabilities in the separation of these positive ions enabled the discovery of stable isotopes of the elements. The first such discovery was with the element neon, which was shown by mass spectrometry to have at least two stable isotopes: 20Ne and 22Ne. Mass spectrometers were used in the Manhattan Project for the separation of isotopes of uranium necessary to create the atomic bomb.

Orbitrap

In mass spectrometry, Orbitrap is an ion trap mass analyzer consisting of an outer barrel-like electrode and a coaxial inner spindle-like electrode that traps ions in an orbital motion around the spindle. The image current from the trapped ions is detected and converted to a mass spectrum using the Fourier transform of the frequency signal.

Electron-transfer dissociation

Electron-transfer dissociation (ETD) is a method of fragmenting multiply-charged gaseous macromolecules in a mass spectrometer between the stages of tandem mass spectrometry (MS/MS). Similar to electron-capture dissociation, ETD induces fragmentation of large, multiply-charged cations by transferring electrons to them. ETD is used extensively with polymers and biological molecules such as proteins and peptides for sequence analysis. Transferring an electron causes peptide backbone cleavage into c- and z-ions while leaving labile post translational modifications (PTM) intact. The technique only works well for higher charge state peptide or polymer ions (z>2). However, relative to collision-induced dissociation (CID), ETD is advantageous for the fragmentation of longer peptides or even entire proteins. This makes the technique important for top-down proteomics. The method was developed by Hunt and coworkers at the University of Virginia.

Gerald Gabrielse is an American physicist. He is the Board of Trustees Professor of Physics and Director of the Center for Fundamental Physics at Northwestern University, and Emeritus George Vasmer Leverett Professor of Physics at Harvard University. He is primarily known for his experiments trapping and investigating antimatter, measuring the electron g-factor, and measuring the electron electric dipole moment. He has been described as "a leader in super-precise measurements of fundamental particles and the study of anti-matter."

Frans Michel Penning

Frans Michel Penning was a Dutch experimental physicist. He received his PhD from the University of Leiden in 1923, and studied low pressure gas discharges at the Philips Laboratory in Eindhoven, developing new electron tubes during World War II. Many detailed observations of gas ionization were done with colleagues, finding notable results for helium and magnetic fields. He made precise measurements of Townsend discharge coefficients and cathode voltage fall. Penning made important contributions to the advancement of high resolution Mass spectrometry.

Hybrid mass spectrometer

A hybrid mass spectrometer is a device for tandem mass spectrometry that consists of a combination of two or more m/z separation devices of different types.

Linear ion trap

The linear ion trap (LIT) is a type of ion trap mass spectrometer. In a linear ion trap, ions are confined radially by a two-dimensional radio frequency (RF) field, and axially by stopping potentials applied to end electrodes. Linear ion traps have high injection efficiencies and high ion storage capacities.

Trojan wave packet wave packet that is nonstationary and nonspreading

A trojan wave packet is a wave packet that is nonstationary and nonspreading. It is part of an artificially created system that consists of a nucleus and one or more electron wave packets, and that is highly excited under a continuous electromagnetic field.

High-precision experiments could reveal small previously unseen differences between the behavior of matter and antimatter. This prospect is appealing to physicists because it may show that nature is not Lorentz symmetric.

Collision-induced dissociation A mass spectrometry technique to induce fragmentation of selected ions in the gas phase

Collision-induced dissociation (CID), also known as collisionally activated dissociation (CAD), is a mass spectrometry technique to induce fragmentation of selected ions in the gas phase. The selected ions are usually accelerated by applying an electrical potential to increase the ion kinetic energy and then allowed to collide with neutral molecules. In the collision some of the kinetic energy is converted into internal energy which results in bond breakage and the fragmentation of the molecular ion into smaller fragments. These fragment ions can then be analyzed by tandem mass spectrometry.

Peter E. Toschek German physicist

Peter E. Toschek was a German experimental physicist who researched nuclear physics, quantum optics, and laser physics. He is known as a pioneer of laser spectroscopy and for the first demonstration of single trapped atoms (ions). He was a professor at Hamburg University.

References

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  20. Magnet for cathode-ray tube ion traps
  21. Ion Trap for a Cathode Ray Tube