Quantum-enhanced sensing of displacements and electric fields with two-dimensional trapped-ion crystals

Abstract

Fully controllable ultracold atomic systems are creating opportunities for quantum sensing, yet demonstrating a quantum advantage in useful applications by harnessing entanglement remains a challenging task. Here, we realize a many-body quantum-enhanced sensor to detect displacements and electric fields using a crystal of ~150 trapped ions. The center-of-mass vibrational mode of the crystal serves as a high-Q mechanical oscillator, and the collective electronic spin serves as the measurement device. By entangling the oscillator and collective spin and controlling the coherent dynamics via a many-body echo, a displacement is mapped into a spin rotation while avoiding quantum back-action and thermal noise. We achieve a sensitivity to displacements of 8.8 ± 0.4 decibels below the standard quantum limit and a sensitivity for measuring electric fields of 240 ± 10 nanovolts per meter in 1 second. Feasible improvements should enable the use of trapped ions in searches for dark matter.

Quantum technology for military applications

“…Besides allowing measurement of gravitational and inertial parameters, it can measure Casimir or van der Waals forces. More recently, using quantum-entangled trapped ions, measurement of electric fields has reached a sensitivity of ∼ 240 nV/ms -1 [103], which is several orders of magnitude better than the classical counterpart.…”

Coherent scattering of low mass dark matter from optically trapped sensors

“…Levitated optomechanical sensors enabling sensitive searches for DM and other weakly coupled phenomena have been demonstrated [16][17][18][19] or proposed [13,[20][21][22][23][24][25]. Extending such systems to large arrays of sensors-a rapidly growing tool in the case of single atoms using optical traps [26][27][28][29][30] or ions using radio-frequency (RF) electric fields or Penning traps [31][32][33], and routine for fluid-levitated spheres [34] -could lead to substantial sensitivity improvements.…”

“…For SiO 2 nanospheres with SQL detection sensitivity and a trapping frequency of 2π × 1 kHz, the optimal sensor size occurs at a diameter of 15 nm, giving ∼ 10 6 nucleons in a sphere and ∼ 12 orders of magnitude enhancement in the scattering cross section compared to a single nucleon. Such objects are commercially available and may be trapped electromagnetically [31][32][33].…”

“…While the required optical power is achievable even for large arrays of such objects, for 15 nm spheres, the lower trap depth may make optical trapping impractical and necessitate the use of RF electromagnetic ("Paul") traps or Penning traps to confine the particles. Such traps are a scalable platform for trapping large numbers of objects [31][32][33], and ongoing work to extend to even larger arrays is driven by quantum computing efforts. Optical detection at the SQL requires detection efficiencies approaching unity.…”

Frustrated Superradiant Phase Transition

“…A superradiant phase transition (SPT) occurs in a system of coupled bosons and spins when the spin-boson coupling strength exceeds a critical value, whereby the bosonic modes exhibit a ground-state superradiance. The Dicke model is a paradigmatic model exhibiting the SPT [12][13][14][15][16][17][18][19][20][21], which describes a single bosonic mode coupled to N a two-level atoms and has been realized in disparate physical systems including cavity QED systems [22][23][24][25][26] and trapped-ions [27][28][29]. The SPTs have also been found in various generalization of the Dicke models including the finite-component systems [30][31][32][33] and lattice systems [34].…”