One of the most ambitious technological goals is the development of devices working under the laws of quantum mechanics. Among others, an important challenge to be resolved on the way to such ...breakthrough technology concerns the scalability of the available Hilbert space. Recently, proof‐of‐principle experiments were reported, in which the implementation of quantum algorithms (the Grover's search algorithm, iSWAP‐gate, etc.) in a single‐molecule nuclear spin qudit (with d = 4) known as 159TbPc2 was described, where the nuclear spins of lanthanides are used as a quantum register to execute simple quantum algorithms. In this progress report, the goal of linear and exponential up‐scalability of the available Hilbert space expressed by the qudit‐dimension “d” is addressed by synthesizing lanthanide metal complexes as quantum computing hardware. The synthesis of multinuclear large‐Hilbert‐space complexes has to be carried out under strict control of the nuclear spin degree of freedom leading to isotopologues, whereby electronic coupling between several nuclear spin units will exponentially extend the Hilbert space available for quantum information processing. Thus, improved multilevel spin qudits can be achieved that exhibit an exponentially scalable Hilbert space to enable high‐performance quantum computing and information storage.
The scalability of molecular spin qudits to act as quantum computing hardware can be expressed by the tuning the dimension parameter “d”. The synthesis of such large‐Hilbert‐space molecular complexes has to occur under strict control of the nuclear spin degree, while electronic coupling between several nuclear spin units can exponentially extend the Hilbert space available for quantum information processing.
Molecular spin qudits for quantum algorithms Moreno-Pineda, Eufemio; Godfrin, Clément; Balestro, Franck ...
Chemical Society reviews,
01/2018, Letnik:
47, Številka:
2
Journal Article
Recenzirano
Presently, one of the most ambitious technological goals is the development of devices working under the laws of quantum mechanics. One prominent target is the quantum computer, which would allow the ...processing of information at quantum level for purposes not achievable with even the most powerful computer resources. The large-scale implementation of quantum information would be a game changer for current technology, because it would allow unprecedented parallelised computation and secure encryption based on the principles of quantum superposition and entanglement. Currently, there are several physical platforms racing to achieve the level of performance required for the quantum hardware to step into the realm of practical quantum information applications. Several materials have been proposed to fulfil this task, ranging from quantum dots, Bose-Einstein condensates, spin impurities, superconducting circuits, molecules, amongst others. Magnetic molecules are among the list of promising building blocks, due to (i) their intrinsic monodispersity, (ii) discrete energy levels (iii) the possibility of chemical quantum state engineering, and (iv) their multilevel characteristics that lead to Qudits, where the dimension of the Hilbert space is
d
> 2. Herein we review how a molecular nuclear spin qu
d
it, (
d
= 4), known as TbPc
2
, gathers all the necessary requirements to perform as a molecular hardware platform with a first generation of molecular devices enabling even quantum algorithm operations.
Molecules are promising building blocks for Quantum information processing. Herein we describe how a molecular multilevel nuclear spin qubit (or qudit, where
d
= 4), known as TbPc
2
, showing all necessary requirements to perform as a molecular hardware platform with a first generation of molecular devices enabling even quantum algorithm operations.
Quantum control of individual spins in condensed-matter devices is an emerging field with a wide range of applications, from nanospintronics to quantum computing. The electron, possessing spin and ...orbital degrees of freedom, is conventionally used as the carrier of quantum information in proposed devices. However, electrons couple strongly to the environment, and so have very short relaxation and coherence times. It is therefore extremely difficult to achieve quantum coherence and stable entanglement of electron spins. Alternative concepts propose nuclear spins as the building blocks for quantum computing, because such spins are extremely well isolated from the environment and less prone to decoherence. However, weak coupling comes at a price: it remains challenging to address and manipulate individual nuclear spins. Here we show that the nuclear spin of an individual metal atom embedded in a single-molecule magnet can be read out electronically. The observed long lifetimes (tens of seconds) and relaxation characteristics of nuclear spin at the single-atom scale open the way to a completely new world of devices in which quantum logic may be implemented.
Magnetic relaxation processes were first discussed for a crystal of paramagnetic transition ions. It was suggested that mechanical vibrations of the crystal lattice (phonons) modulate the crystal ...electric field of the magnetic ion, thus inducing a 'direct' relaxation between two different spin states. Direct relaxation has also been predicted for single-molecule magnets with a large spin and a high magnetic anisotropy and was first demonstrated in a Mn12 acetate crystal. The spin-lattice relaxation time for such a direct transition is limited by the phonon density of states at the spin resonance. In a three-dimensional system, such as a single-molecule magnet crystal, the phonon energy spectrum is continuous, but in a one-dimensional system, like a suspended carbon nanotube, the spectrum is discrete and can be engineered to an extremely low density of states. An individual single-molecule magnet, coupled to a suspended carbon nanotube, should therefore exhibit extremely long relaxation times and the system's reduced size should result in a strong spin-phonon coupling. Here, we provide the first experimental evidence for a strong spin-phonon coupling between a single molecule spin and a carbon nanotube resonator, ultimately enabling coherent spin manipulation and quantum entanglement.
Recent advances in addressing isolated nuclear spins have opened up a path toward using nuclear-spin–based quantum bits. Local magnetic fields are normally used to coherently manipulate the state of ...the nuclear spin; however, electrical manipulation would allow for fast switching and spatially confined spin control. Here, we propose and demonstrate coherent single nuclear spin manipulation using electric fields only. Because there is no direct coupling between the spin and the electric field, we make use of the hyperfine Stark effect as a magnetic field transducer at the atomic level. This quantum-mechanical process is present in all nuclear spin systems, such as phosphorus or bismuth atoms in silicon, and offers a general route toward the electrical control of nuclear-spin–based devices.
Abstract
Quantum technologies are expected to introduce revolutionary changes in information processing in the near future. Nowadays, one of the main challenges is to be able to handle a large number ...of quantum bits (qubits), while preserving their quantum properties. Beyond the usual two-level encoding capacity of qubits, multi-level quantum systems are a promising way to extend and increase the amount of information that can be stored in the same number of quantum objects. Recent work (Kues et al. 2017), has shown the possibility to use devices based on photonic integrated circuits to entangle two qudits (with “d” being the number of available states). In the race to develop a mature quantum technology with real-world applications, many possible platforms are being investigated, including those that use photons, trapped ions, superconducting and silicon circuits and molecular magnets. In this work, we present the electronic read-out of a coupled molecular multi-level quantum systems, carried by a single Tb
2
Pc
3
molecular magnet. Owning two magnetic centres, this molecular magnet architecture permits a 16 dimensions Hilbert space, opening the possibility of performing more complex quantum algorithms.
The classical Einstein-de Haas experiment demonstrates that a change of magnetization in a macroscopic magnetic object results in a mechanical rotation of this magnet. This experiment can therefore ...be considered as a macroscopic manifestation of the conservation of total angular momentum and energy of electronic spins. Since the conservation of angular momentum is a consequence of a system's rotational invariance, it is valid for an ensemble of spins in a macroscopic ferromaget as well as for single spins. Here we propose an experimental realization of an Einstein-de Haas experiment at the single-spin level based on a single-molecule magnet coupled to a nanomechanical resonator. We demonstrate that the spin associated with the single-molecule magnet is then subject to conservation of total angular momentum and energy, which results in a total suppression of the molecule's quantum tunnelling of magnetization.
Abstract
Cooling down nanomechanical force probes is a generic strategy to enhance their sensitivities through the concomitant reduction of their thermal noise and mechanical damping rates. However, ...heat conduction becomes less efficient at low temperatures, which renders difficult to ensure and verify their proper thermalization. Here we implement optomechanical readout techniques operating in the photon counting regime to probe the dynamics of suspended silicon carbide nanowires in a dilution refrigerator. Readout of their vibrations is realized with sub-picowatt optical powers, in a situation where less than one photon is collected per oscillation period. We demonstrate their thermalization down to 32 ± 2 mK, reaching very large sensitivities for scanning probe force sensors, 40 zN Hz
−1/2
, with a sensitivity to lateral force field gradients in the fN m
−1
range. This opens the road toward explorations of the mechanical and thermal conduction properties of nanoresonators at minimal excitation level, and to nanomechanical vectorial imaging of faint forces at dilution temperatures.
Molecular spintronics using single molecule magnets (SMMs) is a fast growing field of nanoscience that proposes to manipulate the magnetic and quantum information stored in these molecules. Herein we ...report evidence of a strong magnetic coupling between a metallic ion and a radical spin in one of the most extensively studied SMMs: the bis(phtalocyaninato)terbium(III) complex (TbPc2). For that we use an original multiterminal device comprising a carbon nanotube laterally coupled to the SMMs. The current through the device, sensitive to magnetic interactions, is used to probe the magnetization of a single Tb ion. Combining this electronic read-out with the transverse field technique has allowed us to measure the interaction between the terbium ion, its nuclear spin, and a single electron located on the phtalocyanine ligands. We show that the coupling between the Tb and this radical is strong enough to give extra resonances in the hysteresis loop that are not observed in the anionic form of the complex. The experimental results are then modeled by diagonalization of a three-spins Hamiltonian. This strong coupling offers perspectives for implementing nuclear and electron spin resonance techniques to perform basic quantum operations in TbPc2.
Superconducting quantum information processing machines are predominantly based on microwave circuits with relatively low characteristic impedance, about 100 Ω, and small anharmonicity, which can ...limit their coherence and logic gate fidelity
. A promising alternative is circuits based on so-called superinductors
, with characteristic impedances exceeding the resistance quantum R
= 6.4 kΩ. However, previous implementations of superinductors, consisting of mesoscopic Josephson junction arrays
, can introduce unintended nonlinearity or parasitic resonant modes in the qubit vicinity, degrading its coherence. Here, we present a fluxonium qubit design based on a granular aluminium superinductor strip
. We show that granular aluminium can form an effective junction array with high kinetic inductance and be in situ integrated with standard aluminium circuit processing. The measured qubit coherence time Formula: see text illustrates the potential of granular aluminium for applications ranging from protected qubit designs to quantum-limited amplifiers and detectors.
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