We report on the preparation and detection of entangled states between an electron spin 1/2 and a nuclear spin 1/2 in a molecular single crystal. These were created by applying pulses at ESR (9.5 GHz) and NMR (28 MHz) frequencies. Entanglement was detected by using a special entanglement detector sequence based on a unitary back transformation including phase rotation.PACS numbers: 03.67.-a, 03.65. Ud, 33.35.+r, The entanglement between two spins 1/2 is at the heart of quantum mechanics. Ever since a so-called "paradox" was formulated by Einstein, Podolsky and Rosen (EPR) [1], referring to local measurements performed on the individual spins of a delocalized entangled pair, properties of entanglement and its consequences for quantum physics has been discussed in great detail [2]. In the context of quantum information processing (QIP) entanglement has been considered as a resource for quantum parallelism (speedup of quantum computing) [3,4,5] and quantum cryptography [6,7]. A number of these quantum algorithms have been demonstrated in NMR (nuclear magnetic resonance) quantum computing [8,9,10].In this contribution we report on the experimental preparation and observation of the entangled states of an electron spin S = 1/2 and a nuclear spin I = 1/2 in a crystalline solid. The spins considered here are a proton and a radical (unpaired electron spin) produced by x-ray irradiation of a malonic acid single crystal [11]. This leads to the partial conversion of the CH 2 group of the malonic acid molecule to the radical• CH where the dot marks the electron spin. In a strong magnetic field the following four Zeeman product states |m S m I = | ↑↑ , | ↑↓ , | ↓↑ , | ↓↓ exist where the arrows label the ±1/2 states of the electron and the nuclear spin. Equivalently we will use a qubit labelling as |m S m I = |00 , |01 , |10 , |11 . The energy level diagram corresponding to the electron-proton spin system is shown in fig. 1, where we have also indicated the possible ESR (∆m S = ±1) and NMR transitions (∆m I = ±1) of the individual spins by solid arrows.What we are aiming at are states of the typeThese represent all four possible entangled states of a two qubit system, also called the Bell states of two spins 1/2. They correspond to a superposition of the states in fig. 1 connected by dashed arrows. Electron spin resonance (ESR) was performed at Xband (9.49 GHz) at T = 40 K. The low temperature was chosen only for reasons of signal-to-noise ratio. The two well resolved ESR lines due to the • CH proton depend on the orientation of the single crystal and were observed at magnetic fields of 338.2 mT and 339.2 mT with a linewidth of 0.5 mT for the ESR and about 1 MHz for the ENDOR (electron nuclear double resonance) line. This orientation corresponds to a principal axis of the hyperfine tensor. There are two different proton NMR transitions. We applied pulsed ENDOR techniques to one of them at the frequency of 28.05 MHz.In the high temperature approximation we express the Boltzmann spin density matrix asρ B = (1 − K B ) 1 41 + K B...

No abstract

We report on new europium, strontium and ytterbium endohedral fullerene cages of the type Eu@C 72 , Sr@C 72 and Yb@C 72 . Single isomers of Eu@C 72 -I, Sr@C 72 -I, Sr@C 72 -II and Yb@C 72 -I were isolated by multi-step HPLC for the first time. Details of their synthesis, separation and characterization by LDI-TOF mass spectrometry and UV-vis will be discussed. Additionally, EPR spectroscopy of Eu@C 72 -I was performed. A second isomer of europium and ytterbium endohedral C 72 , Eu@C 72 -II and Yb@C 72 -II, has been separated by HPLC and identified by LDI-TOF mass spectrometry.

Sc3@C82 has been investigated by X- and W-band EPR. The isotropic and anisotropic hyperfine interaction between the electron spin and the 45Sc nuclei of the Sc3-triangle was evaluated. In addition, a statistical model analyzing the 13C hyperfine coupling of the C82 cage is applied and its consequences for the charge transfer are discussed. The observed EPR line broadening with decreasing temperature was modeled with a simple exchange model, which considers the molecular motion of the Sc3-triangle inside the C82 cage. This allowed the estimation of the linewidth contributions of the hyperfine- and g-anisotropies as well as the temperature dependence of the exchange rate, which increases rapidly with temperature and follows an exponential law.

No abstract