https://biblio.ugent.be/publication/685594/file/1130605.pdf

Review of Particle Physics

This paper gives the 2010 self-consistent set of values of the basic constants and conversion factors of physics and chemistry recommended by the Committee on Data for Science and Technology (CODATA) for international use. The 2010 adjustment takes into account the data considered in the 2006 adjustment as well as the data that became available from 1 January 2007, after the closing date of that adjustment, until 31 December 2010, the closing date of the new adjustment. Further, it describes in detail the adjustment of the values of the constants, including the selection of the final set of input data based on the results of least-squares analyses. The 2010 set replaces the previously recommended 2006 CODATA set and may also be found on the World Wide Web at physics.nist.gov/constants.

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CODATA Recommended Values of the Fundamental Physical Constants: 2006

(b) Write out the equations for the time dependence of ρ11, ρ22, ρ12 and ρ21 assuming that a light field interaction V = -μ12Ee iωt + c.c. couples only levels |1> and |2>, and that the excited levels exhibit spontaneous decay. (8 marks) (c) Under steady-state conditions, find the ratio of populations in states |2> and |3>. (3 marks) (d) Find the slowly varying amplitude ̃ ρ 12 of the polarization ρ12 = ̃ ρ 12e iωt . (6 marks) (e) In the limiting case that no decay is possible from intermediate level |3>, what is the ground state population ρ11(∞)? (2 marks) 2. (15 marks total) In a 2-level atom system subjected to a strong field, dressed states are created in the form |D1(n)> = sin θ |1,n> + cos θ |2,n-1> |D2(n)> = cos θ |1,n> sin θ |2,n-1>

The Quantum Theory of Light

The internet-a vast network that enables simultaneous long-range classical communication-has had a revolutionary impact on our world. The vision of a quantum internet is to fundamentally enhance internet technology by enabling quantum communication between any two points on Earth. Such a quantum internet may operate in parallel to the internet that we have today and connect quantum processors in order to achieve capabilities that are provably impossible by using only classical means. Here, we propose stages of development toward a full-blown quantum internet and highlight experimental and theoretical progress needed to attain them.

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Quantum internet: A vision for the road ahead

/pdf/review-of-particle-physics-1996-1997-jeg703df6k.pdf

Review of Particle Physics, 1996-1997

We present studies of resonance-enhanced photoionization for isotope-selective loading of ${\mathrm{Ca}}^{+}$ into a Paul trap. The ${4s}^{2}{}^{1}{S}_{0}\ensuremath{\leftrightarrow}4s4p{}^{1}{P}_{1}$ transition of neutral calcium is driven by a 423 nm laser and the atoms are photoionized by a second laser at 389 nm. Isotope selectivity is achieved by using crossed atomic and laser beams to reduce the Doppler width significantly below the isotope shifts in the 423 nm transition. The loading rate of ions into the trap is studied under a range of experimental parameters for the abundant isotope ${}^{40}{\mathrm{Ca}}^{+}.$ Using the fluorescence of the atomic beam at 423 nm as a measure of the Ca number density, we estimate a lower limit for the absolute photoionization cross section of 170(60) Mb. We achieve loading and laser cooling of all the naturally occurring isotopes, without the need for enriched sources. Laser heating/cooling is observed to enhance the isotope selectivity. In the case of the rare species ${}^{43}{\mathrm{Ca}}^{+}$ and ${}^{46}{\mathrm{Ca}}^{+},$ which have not previously been laser cooled, the loading is not fully isotope selective, but we show that pure crystals of ${}^{43}{\mathrm{Ca}}^{+}$ may nevertheless be obtained. We find that for loading ${}^{40}{\mathrm{Ca}}^{+}$ the 389 nm laser may be replaced by an incoherent source.

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Isotope-selective photoionization for calcium ion trapping

We report a measurement of the lifetime of the $3d{}^{2}{D}_{5/2}$ metastable level in ${}^{40}{\mathrm{Ca}}^{+},$ using quantum jumps of a single cold calcium ion in a linear Paul trap. The $4s{}^{2}{S}_{1/2}--3d{}^{2}{D}_{5/2}$ transition is significant for single-ion optical frequency standards, astrophysical references, and tests of atomic structure calculations. We obtain $\ensuremath{\tau}=1.168\ifmmode\pm\else\textpm\fi{}0.007$ s from observation of nearly $64000$ quantum jumps during $\ensuremath{\sim}32$ h. Our result is more precise and significantly larger than previous measurements. Experiments carried out to quantify systematic effects included a study of a previously unremarked source of systematic error, namely, excitation by the broad background of radiation emitted by a semiconductor diode laser. Combining our result with atomic structure calculations yields $1.20\ifmmode\pm\else\textpm\fi{}0.01$ s for the lifetime of $3d{}^{2}{D}_{3/2}.$ We also use quantum jump observations to demonstrate photon antibunching, and to estimate background pressure and heating rates in the ion trap.

Measurement of the lifetime of the 3 d 2 D 5 / 2 state in 40 Ca +

Web summaryHarnessing the entanglement of different ionic species could bring new flexibility in quantum computing, and now two groups independently demonstrate entanglement between different atomic species; Ballance et al. achieve entanglement between different atomic isotopes, whereas the related paper by Tan et al. shows entanglement between different elements, together demonstrating a first step towards mixed-species quantum logic. In quantum-computing architectures, not all physical systems are equally good at completing each task. For example, in trapped-ion quantum computers, one specific element might be an excellent memory qubit, while another element is more suited to transporting information between nodes. However, a crucial prerequisite to harness these advantages is the entanglement of different atomic species. Now, two groups have independently achieved this. Ting Rei Tan et al. showed entanglement between different elements 9Be+ and 25Mg+, and Christopher Ballance et al. achieved entanglement between different atomic isotopes, 40Ca+ and 43Ca+. These studies represent a first step towards mixed-species quantum logic, and from a fundamental perspective they show that particles that are distinguishable by many internal properties can indeed be entangled and violate Bell's inequality. Entanglement is one of the most fundamental properties of quantum mechanics1,2,3, and is the key resource for quantum information processing4,5 (QIP). Bipartite entangled states of identical particles have been generated and studied in several experiments, and post-selected or heralded entangled states involving pairs of photons, single photons and single atoms, or different nuclei in the solid state, have also been produced6,7,8,9,10,11,12. Here we use a deterministic quantum logic gate to generate a ‘hybrid’ entangled state of two trapped-ion qubits held in different isotopes of calcium, perform full tomography of the state produced, and make a test of Bell’s inequality with non-identical atoms. We use a laser-driven two-qubit gate13, whose mechanism is insensitive to the qubits’ energy splittings, to produce a maximally entangled state of one 40Ca+ qubit and one 43Ca+ qubit, held 3.5 micrometres apart in the same ion trap, with 99.8 ± 0.6 per cent fidelity. We test the CHSH (Clauser–Horne–Shimony–Holt)14 version of Bell’s inequality for this novel entangled state and find that it is violated by 15 standard deviations; in this test, we close the detection loophole8 but not the locality loophole7. Mixed-species quantum logic is a powerful technique for the construction of a quantum computer based on trapped ions, as it allows protection of memory qubits while other qubits undergo logic operations or are used as photonic interfaces to other processing units15,16. The entangling gate mechanism used here can also be applied to qubits stored in different atomic elements; this would allow both memory and logic gate errors caused by photon scattering to be reduced below the levels required for fault-tolerant quantum error correction, which is an essential prerequisite for general-purpose quantum computing.

Hybrid quantum logic and a test of Bell's inequality using two different atomic isotopes.

We report the results of a laser experiment to search for the parity-nonconserving optical rotation in atomic bismuth. We work at wavelengths close to the 648-nm J=32 — J=52 M1 transition from the ground state. We find R=Im(E1M1)=(+2.7±4.7)×10−8, in disagreement with the theoretical value R=−30×10−8 predicted for this transition on the basis of the Weinberg-Salam model of the weak interactions combined with relativistic central-field atomic theory.

Search for Parity-Nonconserving Optical Rotation in Atomic Bismuth

We report the first precise measurements of parity nonconserving (PNC) optical rotation in atoms, carried out on the 876-nm M1 transition in bismuth. We obtain ${\mathit{R}}_{\mathit{i}}$=Im(E${1}_{\mathrm{PNC}}^{\mathit{i}}$/M1)=(-10.12\ifmmode\pm\else\textpm\fi{}0.20)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$, where E${1}_{\mathrm{PNC}}^{\mathit{i}}$ is the E1 amplitude mixed into the transition by the nuclear spin-independent PNC interaction. The result is in excellent agreement with the standard model of the electroweak interaction. The amplitude of nuclear spin-dependent PNC rotation is found to be less than 1.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}2}$ of that due to the nuclear spin-independent interaction.

D. N. Stacey

Papers

Isotope-selective photoionization for calcium ion trapping

Measurement of the lifetime of the 3 d 2 D 5 / 2 state in 40 Ca +

Hybrid quantum logic and a test of Bell's inequality using two different atomic isotopes.

Search for Parity-Nonconserving Optical Rotation in Atomic Bismuth

Precise measurement of parity nonconserving optical rotation at 876 nm in atomic bismuth.