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We propose a novel physical realization of a quantum computer. The qubits are electric dipole moments of ultracold diatomic molecules, oriented along or against an external electric field. Individual molecules are held in a 1-D trap array, with an electric field gradient allowing spectroscopic addressing of each site. Bits are coupled via the electric dipole-dipole interaction. Using technologies similar to those already demonstrated, this design can plausibly lead to a quantum computer with > ∼ 10 4 qubits, which can perform ∼ 10 5 CNOT gates in the anticipated decoherence time of ∼ 5 s.PACS numbers: 03.67. Lx, 33.80.Ps, 33.55.Be We describe a new technical approach to the design of a quantum computer (QC). The basic QC architecture is shown in Fig. 1. The qubits consist of the electric dipole moments of diatomic molecules, oriented along or against an external electric field. Bits are coupled by the electric dipole-dipole interaction. Individual molecules are held in a 1-D trap array, with an electric field gradient allowing spectroscopic addressing of each site. Loading with ultracold molecules makes it possible to use a weak trapping potential, which should allow long decoherence times for the system. This design bears various features in common with other recent proposals which employ electric dipole couplings [1,2,3]. However, the technical parameters of our design appear very favorable, and apparently only incremental improvements of demonstrated techniques are required in order to build a QC of unprecedented size.We describe the molecular qubits as permanent electric dipoles oriented along (|0 ) or against (|1 ) an external electric field ( E ext ). (This model reproduces the exact behavior well in a certain regime.) Lattice sites are equally spaced in the x-direction and each contains one molecule, prepared initially in its ground state |0 . The external field is perpendicular to the trap axis and consists of a constant bias field plus a linear gradient:, where H 0 is the internal energy of a bit, d a is the electric dipole moment of bit a, and E a = E ext (x a ) + E int (x a ) is the total electric field at x a . The internal field E int is created by the electric dipole moments of neighboring bits:The scheme for gate operations is as outlined for the electric dipole moments of quantum dots in Ref. [1]. Transitions between qubit states can be driven by electric resonance, either directly in the microwave region or indirectly by an optical stimulated Raman process. Resonant drive pulses are tuned to frequency ν a = ν 0 + d ef f E a /h, where hν 0 is the difference in internal energies between states |0 and |1 in zero field; the effective dipole momentis the dipole moment in state |0 (|1 ); and h is Planck's constant. Pulses of sufficient temporal length to resolve the energy splitting due to E int can be used for CNOT gates; shorter pulses suffice for one-bit rotations. Final-state readout can be accomplished by state-selective, resonant multiphoton ionization [4] and imaging detection of the resulti...

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We present the result of our most recent search for T-violation in 205 Tl, which is interpreted in terms of an electric dipole moment of the electron de. We find de = (6.9 ± 7.4) × 10 −28 e cm. The present apparatus is a major upgrade of the atomic beam magnetic-resonance device used to set the previous limit on de. PACS numbers: 11.30.Er, 14.60.Cd, 32.10.Dk We report a new result in the search for the electric dipole moment (EDM) of the electron, a quantity of interest in connection with CP violation and extensions to the standard model of particle physics [1][2][3]. In heavy paramagnetic atoms an electron EDM results in an atomic EDM enhanced by a factor R ≡ d atom /d e . Thus we search for a permanent EDM of atomic thallium in the 6 2 P 1/2 F = 1 ground state, where R −585 [4]. Experimental MethodLike its predecessor [5,6], the new experiment [7] uses magnetic resonance with two oscillating rf fields [8] separated by a space containing an intense electric field E, and employs laser optical pumping for state selection and analysis. To control systematic effects arising from motional magnetic fields E × v/c, the previous experiment employed a single pair of counterpropagating vertical atomic beams. The present experiment has two pairs separated by 2.54 cm, each consisting of Tl and Na (see Fig.1). The spatially separated beams are nominally exposed to identical magnetic but opposite electric fields; this provides common-mode noise rejection and control of some systematic effects. Sodium serves as a comagnetometer: it is susceptible to the same systematic effects but insensitive to d e , since R is roughly proportional to the cube of the nuclear charge. Furthermore, sodium's two 3 2 S 1/2 ground state hyperfine levels F =2, 1 have g F = ±1/2, which in principle permits the separation of two different types of motional field effects. Figure 1 shows a schematic diagram of the experiment with the up beams active. Atoms leave the trichamber oven thermally distributed among the ground state hyperfine levels. After some collimation they enter the quantizing magnetic field B, nominally in theẑ direction and typically 0.38 Gauss. Laser beams then depopulate the states with non-zero magnetic quantum numbers m F . Thus, in the first optical region 590 nm z polarized light selects the m F = 0 Zeeman sublevel of either the F = 2 or the F = 1 Na ground state. (B Tl cos ω Tl t + B Na cos ω Na t)x, where 2B Tl = B Na and 1.506ω Tl ω Na . These resonant fields apply 'π/2' pulses, creating coherent superpositions of the m F = 0 states of each species. The atoms then move into the electric field, nominally parallel or anti-parallel to B. Typically |E| = 1.23 × 10 5 V/cm. The second rf field is coherent with the first, differing only by a relative phase shift α. In the analysis regions the atoms are probed with the same laser that performed the state selection. Fluorescence photons accompanying the atomic decays are reflected by polished aluminum paraboloids into Winston cones [9] made of UV-transmitting plastic. These lightpi...