Magnetic-tip trap system

Abstract

We report a detailed theoretical model of recently-demonstrated magnetic trap system based on a pair of magnetic tips. The model takes into account key parameters such as tip diameter, facet angle and gap separation. It yields quantitative descriptions consistent with experiments such as the vertical and radial frequency, equilibrium position and the optimum facet angle that produces the strongest confinement. We arrive at striking conclusions that a maximum confinement enhancement can be achieved at an optimum facet angle θmax = arccos 2/3 and a critical gap exists beyond which this enhancement effect no longer applies. This magnetic trap and its theoretical model serves as a new and interesting example of a simple and elementary magnetic trap in physics. PACS numbers: 04.60.BcVarious electromagnetic trap systems play important role in physics for their ability to trap and isolate particles or matter that have produced many applications and discoveries. Examples are Penning trap [1, 2], optical dipole trap or optical tweezer [3][4][5], magneto optic trap [6,7] and various diamagnetic traps [8][9][10][11][12]. For diamagnetic trap systems, high field-gradient product (B ∇B) is necessary to achieve trapping or levitation [13]. A new approach is to use magnetic tip geometry as recently demonstrated by O'Brien et al. [14]. The tip geometry maximizes B ∇B at the trapped object that leads to stronger field confinement, thus high frequency and high quality factor (Q). This characteristics is of high interest for research that explores macroscopic limits of classical mechanics and quantum mechanics. Such magnetic trap also offers interesting alternative to optical trap as the latter can lead to excessive heating and encounters instabilities in vacuum [15]. The ability to achieve high magnetic field gradients in a localized position using magnetic tip is also useful for other applications such as for nuclear magnetic resonant imaging [16] and magnetic force microscopy [17].Currently, there is strong interest in magnetic trap system for various applications such as precision gravimetry [18], study of displacement and velocity of Brownian particle [19], gas temperature measurement [20], and research that explores the boundaries of the classical and quantum systems. For example, trapped nanodiamond can be used to investigate the quantum mechanical properties such as superposition of states [21,22], control of electron spin of nanodiamond nitrogen-vacancy centers and to observe the electron spin resonance properties [23]. Such a trap could also serve an important role to test quantum mechanical properties of gravity [24,25].In the recent demonstration of a magnetic tip trap O'Brien et al. uses two cylindrical magnets with sharpened tips and a microdiamond as the trapped object [14]. The tips are separated by a gap d = 2a as shown in Fig. 1(a). The trapping occurs due to diamagnetic repulsion that balances the gravity of the diamond and the cylindrical symmetry that produces a stable potential confinement in three dimension. ...

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Enhanced spin-mechanical interaction with levitated micromagnets

“…Optical, electrical, and magnetic levitation are the three types of suspending setups that can all work in a vacuum environment. The magnetic trap with a passive field [43][44][45][46][47][48][49][50][51][52][53][54][55][56] is simpler than the optical trap with lasers [57][58][59][60] and the electrical trap with radio-frequency modulation of a high voltage electric field [31][32][33][34]. Photon recoil, damage to suspended particles caused by the laser's thermal effect, and clamping losses can all be avoided via magnetostatic field levitation [56].…”

“…For these suspended schemes, the suspension objectives are diverse. Glass spheres [59], superconductor spheres [62], superconductor rings [46,67], magnetic microspheres [42,43], silicon particles [58,64] and diamond particles [54][55][56][57] have all been investigated on various platforms. Because of their isolation, they have been used to con- * lipengbo@mail.xjtu.edu.cn struct ultra-sensitive sensors [42,43] as well as to couple superconducting circuits [48] and solid-state spins [15,34,64].…”