Adiabatic quantum state manipulation of single trapped atoms

Abstract

We use microwave induced adiabatic passages for selective spin flips within a string of optically trapped individual neutral Cs atoms. We position-dependently shift the atomic transition frequency with a magnetic field gradient. To flip the spin of a selected atom, we optically measure its position and sweep the microwave frequency across its respective resonance frequency. We analyze the addressing resolution and the experimental robustness of this scheme. Furthermore, we show that adiabatic spin flips can also be induced with a fixed microwave frequency by deterministically transporting the atoms across the position of resonance.PACS numbers: 03.67.Lx, 39.25.+k, 32.80.Qk Adiabatic passages (APs) [1] are an interesting alternative to purely resonant interaction for controlling the quantum state of atoms. They rely on the fact that the coupled atom-field system remains in its instantaneous eigenstate if the variation of its parameters (atomfield detuning and field strength) is sufficiently slow and smooth. One can thus adiabatically transfer a system from an initial to a final state and, under certain conditions, fluctuations of the parameters will not affect the outcome of the AP. The pioneering works concerning APs were performed in nuclear magnetism to achieve inversion of a spin system [2]. The first application of this method in the optical domain was realized in [3] to invert the population in NH 3 molecules. Ever since, a multitude of different AP techniques have been proposed and successfully realized [4]. It has also been shown that APs can be used to robustly prepare superpositions of energy eigenstates [5]. Furthermore, it was proposed to prepare entanglement and implement quantum logic operations through adiabatic processes [6,7].We have recently demonstrated that a string of neutral Cs atoms stored in a standing wave optical dipole trap can be used to realize a quantum register [8]. There, quantum information was written into the two Cs hyperfine ground states by subjecting selected atoms to resonant microwave pulses. Here, we report on the realization of an adiabatic method for flipping the states of individual atoms out of a string. As in [8], the atoms are discriminated through a position dependent transition frequency. The APs are accomplished by sweeping the microwave frequency across the resonance frequency of the respective atom. We investigate the performance of our method by recording AP spectra of few as well as of single atoms, yielding high-quality data in perfect agreement with theory. The spatial discrimination of this scheme is comparable to resonant addressing. At the same time, the method is much more robust than in the resonant case. It is therefore a useful tool for the manipulation and control of our quantum register.Combining fixed frequency microwave pulses with our "optical conveyor belt" technique [9, 10] inside a magnetic field gradient, we furthermore realize APs by transporting atoms across the position of resonance. In this experiment, the atom-field coupling and the ...

Microwave control of atomic motional states in a spin-dependent optical lattice

“…In the same vein of engineering motional states, we project the state |↓, n = 0 onto a shifted potential to create the state |α =T ∆x |↑, n = 0 = e αa † −α * a |↑, n = 0 (32) with α = η x . We realize this by applying an optical repumping pulse while the lattice is displaced by ∆x.…”

Microwave preparation of two-dimensional fermionic spin mixtures

“…The value of the magnetic field gradient and the spacing of the lattice layers induce a limit to the available frequency range, and we need to restrict our frequency sweeps of the microwave transitions to a few kHz. We use hyperbolic secant pulses (HS1) [23] to drive adiabatic passages [27] with flat transfer windows and sharp spectral edges. During an HS1 pulse the frequency detuning δ i (t) and the coupling amplitude Ω i (t) change according to…”

“…Here we report on such a microwave-based preparation technique that allows us to prepare a mixture of two magnetic states of fermionic potassium in a single antinode of a red-detuned optical lattice, in our quantum-gas microscope apparatus. The procedure relies on a sequence of adiabatic microwave transfer pulses [23] in a magnetic field gradient, which are optimized for efficiency and speed. Compared to the technique used in our previous publication [4], the scheme presented here introduces several new features, such as the simultaneous use of two spin states, the visualization of magnetic field gradients and the use of microwave transfers instead of optical pulses, whenever possible.…”

Qubit fidelity of a single atom transferred among the sites of a ring optical lattice

“…For quantum computing with neutral atoms, qubits are encoded in the internal states of single atoms, and each atom is confined in one site of an optical lattice. Quantum registers are initialized by loading single atoms into the optical lattice from cold or ultracold atom ensembles [4,5], The readout is realized by detecting and addressing the lattice with single site resolution [6][7][8][9], Meanwhile, by manipulating the hyperfine states with microwave or stimulated Raman tran sitions, single-qubit operation is easy to implement [4,[10][11][12], Recently, two-qubit gates have been performed with single atoms in two neighbor tweezers utilizing Rydberg blockade [13][14][15], and with many pairs of atoms in the lattices via controlled ground-state collisions [16][17][18]. However, quantum gate between arbitrary pairs of qubits in scalable registers has not been demonstrated.…”