The successful development of a quantum computer would change the world, and current internet encryption methods would cease to function. However, no working quantum computer that even begins to rival conventional computers has been developed yet, which is due to the lack of suitable quantum bits. A key characteristic of a quantum bit is the coherence time. Transition metal complexes are very promising quantum bits, owing to their facile surface deposition and their chemical tunability. However, reported quantum coherence times have been unimpressive. Here we report very long quantum coherence times for a transition metal complex of 68 ms at low temperature (qubit figure of merit Q M ¼ 3,400) and 1 ms at room temperature, much higher than previously reported values for such systems. We show that this achievement is because of the rigidity of the lattice as well as removal of nuclear spins from the vicinity of the magnetic ion.

We report pulsed electron paramagnetic resonance investigations on [(CuL) 3 (OH)](ClO 4 ) 2 · H 2 O, where HL = (E)-2-((3-(methylamino)propylimino) methyl)phenol, to assess its suitability as a qubit. We measured spin-lattice relaxation times up to T 1 = 698(2) μs at 5 K in methanolic frozen solution. The spin-lattice relaxation is driven by the direct process. The phase memory time was determined to be up to T m = 1290(3) ns in methanolic frozen solution and T m = 392(5) ns in powder at 5 K, respectively. By means of both continuous waves and pulsed ENDOR spectroscopy, interactions to protons, nitrogen and copper nuclei were observed. The couplings to the protons were shown to be due to dipolar and through bond interactions.

Controlling the charges and spins of molecules lies at the heart of spintronics. A photoswitchable molecule consisting of two independent spins separated by a photoswitchable moiety was designed in the form of new ligand H L, which features a dithienylethene photochromic unit and two lateral coordinating moieties, and yields molecules with [MM⋅⋅⋅MM] topology. Compounds [M L (py) ] (M=Cu, 1; Co, 2; Ni, 3; Zn, 4) were prepared and studied by single-crystal X-ray diffraction (SCXRD). Different metal centers can be selectively distributed among the two chemically distinct sites of the ligand, and this enables the preparation of many double-spin systems. Heterometallic [MM'⋅⋅⋅M'M] analogues with formulas [Cu Ni L (py) ] (5), [Co Ni L (py) ] (6), [Co Cu L (py) ] (7), [Cu Zn L (py) ] (8), and [Ni Zn L (py) ] (9) were prepared and analyzed by SCXRD. Their composition was established unambiguously. All complexes exhibit two weakly interacting [MM'] moieties, some of which embody two-level quantum systems. Compounds 5 and 8 each exhibit a pair of weakly coupled S=1/2 spins that show quantum coherence in pulsed Q-band EPR spectroscopy, as required for quantum computing, with good phase memory times (T =3.59 and 6.03 μs at 7 K). Reversible photoswitching of all the molecules was confirmed in solution. DFT calculations on 5 indicate that the interaction between the two spins of the molecule can be switched on and off on photocyclization.

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