Abstract
Spins confined in quantum dots are considered as a promising platform for quantum information processing. While many advanced quantum operations have been demonstrated, experimental as well as theoretical efforts are now focusing on the development of scalable spin quantum bit architectures. One particularly promising method relies on the coupling of spin quantum bits to microwave cavity photons. This would enable the coupling of distant spins via the exchange of virtual photons for two qubit gate applications, which still remains to be demonstrated with spin qubits. Here, we use a circuit QED spin–photon interface to drive a single electronic spin in a carbon nanotube-based double quantum dot using cavity photons. The microwave spectroscopy allows us to identify an electrically controlled spin transition with a decoherence rate which can be tuned to be as low as 250 kHz. We show that this value is consistent with the expected hyperfine coupling in carbon nanotubes. These coherence properties, which can be attributed to the use of pristine carbon nanotubes stapled inside the cavity, should enable coherent spin–spin interaction via cavity photons and compare favorably to the ones recently demonstrated in Si-based circuit QED experiments. Our clean and controlled nano-assembly technique of carbon nanotubes in the cavity could be further improved by purified 12C growth to get rid of the nuclear spins resulting in an even higher spin coherence.
Highlights
The observation of strong coupling between the charge or the spin confined in a quantum dot circuit and cavity photons has been reported very recently,[1,2,3,4,5,6] bringing closer the demonstration of distant single spin–single spin interaction,[7,8,9,10,11,12,13] in the quest for scalable quantum information processing platforms.[14]
From the gate dependence of the decoherence rate, we show that the charge noise is the main source of decoherence for the spin when the qubit states are mixed charge/spin states, but that it can be substantially reduced in the spin qubit regime
In order to specify the decoherence mechanism explaining the linewidth found for our spin transition, we have measured the dependence of the decoherence rate as a function of the detuning εδ
Summary
The observation of strong coupling between the charge or the spin confined in a quantum dot circuit and cavity photons has been reported very recently,[1,2,3,4,5,6] bringing closer the demonstration of distant single spin–single spin interaction,[7,8,9,10,11,12,13] in the quest for scalable quantum information processing platforms.[14]. An alternative wording is to state that the ferromagnetic electrodes give rise to a two-site artificial spin–orbit coupling, which makes the spin sensitive to the cavity electric field.[20] It is interesting to note that such an “orbitally” mediated spin–photon coupling allows one to increase the natural spin–photon coupling by about 5 orders of magnitude[4,5,20] without degrading substantially the inherent good coherence properties of a single spin if the device is used in the limit where the electron is trapped almost completely in one of the two dots (left or right) This regime can be reached by detuning the left dot orbital energy εL The dependence of the phase contrast Δφ as a function of εδ which has maxima/minima of about ±15° provides an estimate of the charge coupling strength gC ≈ 2π(21 ± 1) MHz and of the charge decay rate γC ≈ 2π(1.35 ± 0.16) GHz
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