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1. Making qubits from magnetic molecules

   https://doi.org/10.1063/pt.keiz.kcmn  

   Hill, Stephen (February 2025, Physics Today)

   Bottom-up synthesis of such molecules provides physicists with a rich playground to study newly discovered quantum effects and a means to store information at the scale of individual atoms. 

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2. Semiconductor spin qubits

   https://doi.org/10.1103/RevModPhys.95.025003  

   Burkard, Guido; Ladd, Thaddeus D.; Pan, Andrew; Nichol, John M.; Petta, Jason R. (June 2023, Reviews of Modern Physics)
3. Spontaneously interacting qubits from Gauss-Bonnet

   https://doi.org/10.1007/JHEP02(2024)007  

   Prudhoe, Sean; Kumar, Rishabh; Shandera, Sarah (February 2024, Journal of High Energy Physics)

   A<sc>bstract</sc> Building on previous constructions examining how a collection of small, locally interacting quantum systems might emerge via spontaneous symmetry breaking from a single-particle system of high dimension, we consider a larger family of geometric loss functionals and explicitly construct several classes of critical metrics which “know about qubits” (KAQ). The loss functional consists of the Ricci scalar with the addition of the Gauss-Bonnet term, which introduces an order parameter that allows for spontaneous symmetry breaking. The appeal of this method is two-fold: (i) the Ricci scalar has already been shown to have KAQ critical metrics and (ii) exact equations of motions are known for loss functionals with generic curvature terms up to two derivatives. We show that KAQ critical metrics, which are solutions to the equations of motion in the space of left-invariant metrics with fixed determinant, exist for loss functionals that include the Gauss-Bonnet term. We find that exploiting the subalgebra structure leads us to natural classes of KAQ metrics which contain the familiar distributions (GUE, GOE, GSE) for random Hamiltonians. We introduce tools for this analysis that will allow for straightfoward, although numerically intensive, extension to other loss functionals and higher-dimension systems. 

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4. Quantum control of spin qubits using nanomagnets

   https://doi.org/10.1038/s42005-022-01041-8  

   Niknam, Mohamad; Chowdhury, Md. Fahim F.; Rajib, Md Mahadi; Misba, Walid Al; Schwartz, Robert N.; Wang, Kang L.; Atulasimha, Jayasimha; Bouchard, Louis-S. (November 2022, Communications Physics)

   Abstract Single-qubit gates are essential components of a universal quantum computer. Without selective addressing of individual qubits, scalable implementation of quantum algorithms is extremely challenging. When the qubits are discrete points or regions on a lattice, selectively addressing magnetic spin qubits at the nanoscale remains a challenge due to the difficulty of localizing and confining a classical divergence-free field to a small volume of space. Herein we propose a technique for addressing spin qubits using voltage-control of nanoscale magnetism, exemplified by the use of voltage control of magnetic anisotropy. We show that by tuning the frequency of the nanomagnet’s electric field drive to the Larmor frequency of the spins confined to a nanoscale volume, and by modulating the phase of the drive, single-qubit quantum gates with fidelities approaching those for fault-tolerant quantum computing can be implemented. Such single-qubit gate operations require only tens of femto-Joules per gate operation and have lossless, purely magnetic field control. Their physical realization is also straightforward using foundry manufacturing techniques. 

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5. Semiconductor qubits in practice

   https://doi.org/10.1038/s42254-021-00283-9  

   Chatterjee, Anasua; Stevenson, Paul; De Franceschi, Silvano; Morello, Andrea; de Leon, Nathalie P.; Kuemmeth, Ferdinand (March 2021, Nature Reviews Physics)