Decoherence of a Single-Ion Qubit Immersed in a Spin-Polarized Atomic Bath

Abstract

We report on the immersion of a spin-qubit encoded in a single trapped ion into a spin-polarized neutral atom environment, which possesses both continuous (motional) and discrete (spin) degrees of freedom. The environment offers the possibility of a precise microscopic description, which allows us to understand dynamics and decoherence from first principles. We observe the spin dynamics of the qubit and measure the decoherence times (T1 and T2), which are determined by the spin-exchange interaction as well as by an unexpectedly strong spin-nonconserving coupling mechanism.PACS numbers: 03.67.-a 03.65.Yz 37.10.Ty A spin-1/2 system represents the most fundamental quantum mechanical object. Its spin-dynamics anddecoherence when interacting with an environment determine its potential use as a qubit and are responsible for a multitude of impurity effects encountered in the solid state. While an extensive amount of theoretical work on this problem exists (for reviews see [1, 2]), experiments with well-controlled and adjustable environments are scarce. The necessary sensitivity to probe single spins, ideally with a single-shot readout, is often incompatible with the ability to adjust the properties of the environment. Among the few examples of controlled decoherence processes are the quantum measurement process [3], the decoherence of motional quantum states of trapped ions by noisy classical electric fields [4], and the effects of spontaneous emission [5][6][7]. These are related to spin-boson physics, where the environment is formed by a set of harmonic oscillator modes [1]. On the contrary, the decoherence of a localized spin impurity inside an environment of other spins lies at the heart of the so-called central-spin problem [2]. Here, the occurring decoherence mechanisms are different from spinboson physics since the spectrum of the bath is discrete and spin-spin or spin-orbit interactions play a role. The central-spin model has been often applied as a simplified and approximate description of the interaction of semiconductor quantum dots [8] and color centres in solids [9] with their environment.Here we investigate the model system of a single localized spin-1/2 coupled to an spin-polarized environment of tunable density. Specifically, we embed a trapped single Yb + ion, initially laser-cooled to Doppler temperature, into a spin-polarized ultracold neutral bath of 87 Rb atoms and study the resulting decoherence of the ion's internal spin state. We observe an intricate decoherence mechanism, which is spin-nonconserving and involves the coupling of the orbital degrees of freedom with the spin degrees of freedom. We measure the longitudinal (T 1 ) and the transverse (T 2 ) coherence times, also with respect to the energy separation, and identify the time scales for Zeeman-and hyperfine-state relaxation. Level structure of the Yb + electronic ground state in a weak magnetic field. To implement the spin-1/2 system, we use either the Zeeman qubit |mJ = ±1/2 in the isotope 174 Yb + or the magnetic field insensitive hype...

Ground-state properties of ultracold trapped bosons with an immersed ionic impurity

“…Even the inclusion of spin degrees of freedom is possible in our method allowing for the study of a single-ion qubit in an atomic bath as recently reported in Ref. [20]. Finally, one could extend the setup to multiple ions making it possible, for instance, to investigate the polaron physics emerging in such hybrid systems.…”

“…Exploiting the state-dependent atom-ion interaction allows for the realization of quantum gates such * jschurer@physnet.uni-hamburg.de that the advantages of charged and neutral particles are combined [17] or makes it possible to control the tunneling in a bosonic Josephson junction such that the generation of entanglement between the atomic system and a single ion can be engineered [18,19]. Moreover, such systems offer possibilities to investigate and understand spin-decoherence processes and spin-exchange interactions at the fundamental level [20], aiming at negligible spin relaxation and efficient spin-exchange as desirable features for quantum information science. Besides, atom-ion systems are an excellent platform to simulate condensed-matter systems and Fröhlich polaron Hamiltonians more closely [21].…”

Confinement-induced resonances in ultracold atom-ion systems

“…We derived formulas for the atom-ion CIR position (8) and (10) for a fixed atomic wave-number k = m A E / and numerically investigated their applicability in the region 0 ≤ E ≤ 2 ω ⊥ , namely up to the threshold for transverse atomic excitation. We note that these formulae are also applicable for atom-atom CIRs, where the inter-particle interaction is even more short-range.…”

“…The interest in combining in the laboratory ultracold atoms and ions is increased considerably in the last few years [1][2][3][4][5][6][7][8][9][10][11][12]. Their combination defines indeed a new quantum system characterised by an interaction with different energy and length scales with respect to ultracold atoms, which allows to study the formation of molecular ions [13,14], polarons [15], density bubbles [16], mesoscopic entanglement [17,18], novel ground state properties [19] and collective excitations [20], and quantum information processing [21][22][23].…”

Rabi oscillations, decoherence, and disentanglement in a qubit–spin-bath system

“…The quantum dynamics of a single qubit or central spin coupled to a spin environment [1] has been widely studied theoretically in several different areas, including quantum information sciences [2][3][4][5][6][7][8][9], quantum decoherence [10][11][12][13][14][15][16][17][18][19], and excitation energy transfer [20][21][22]. One of the most promising candidates for quantum computation, solidstate spin systems, are inevitably coupled to their surrounding environment, usually through interactions with neighboring nuclear spins [6,23,24].…”