Quantum Computer with Superconductivity at Room Temperature

Qubits and Superconductivity

The basic unit of quantum computing, a quantum bit or qubit, can also be 0 or 1 – or both at the same time. A qubit’s information is denoted by its spin property: up, down or a superposition of both.

Superconductivity is one of the most promising approaches to quantum computing because it offers devices with little dissipation, ultrasensitive magnetometers, and electrometers for state readout, large-scale-integration, and a family of classical electronics that could be used for quantum bit (qubit) control. The qubits are implemented in nanoscale dimensions, such as spintronic, single-electron devices and ultra-cold gas of Bose-Einstein condensate state devices. Two of the most successful realizations of solid state qubits are: spin-qubits and superconducting qubits. We have discussed Spin-orbit Coupling Qubits for Quantum Computing and AI.

Superconductivity quantum computing, attempting to define and address the qubits on a chip, much like the transistors which are now packed into an integrated circuit on a silicon microprocessor. A distinguishing feature of superconducting quantum circuits is the usage of a Josephson junction – an electrical element non existent in normal conductors. The energy levels of the superconducting qubit are tunable and tailorable via lithography of the Josephson junctions. Another benefit of the superconducting qubit architecture is the all-electrical control using standard microwave and radio-frequency (RF) engineering techniques.

In superconductive material the total spin of a Cooper pair is an integer number, thus the Cooper pairs are bosons (while the single electrons in the normal conductor are fermions). Cooled bosons, contrary to cooled fermions, are allowed to occupy a single quantum energy level, in an effect known as the Bose-Einstein condensate. When two particles are entangled, they act as if they’re connected. In a Bose-condensate all the particles move consistently. They form one quantum-mechanical wave and behave like one huge particle. All of them are located in one and the same place and at the same time each of them is “spread” over the whole region of space.

Topological quantum computation (TQC):

The key idea of TQC is to encode qubits into states of topological phases of matter.  In 2010, researchers realized that the combination of rather conventional ingredients, such as special semiconductors, superconductors, and magnetic fields, could result in one such phase—a topological superconductor. The topological superconductors, or Majorana nanowires as they are often called are used to store quantum information nonlocally, they are protected from noise, and have been proposed as a building block for a quantum computer.

Phase Qubits based on Josephson junctions

Phase qubit is a superconducting device based on the superconductor-insulator-superconductor Josephson junction, designed to operate as a quantum bit, or qubit. The phase qubit is closely related, yet distinct from, the flux qubit and the charge qubit. Josephson junction is basically sandwiching a thin layer of a non-superconducting material between two layers of superconducting material. A Josephson junction is a tunnel junction, made of two pieces of superconducting metal separated by a very thin insulating barrier, about 1 nm in thickness.

Cooper pairs can “tunnel” through the Josephson junction from one island to the other. This tunneling gives rise to a current. The charge and phase differences the essential parameters describing the properties of the Josephson junctions.  Phase qubits are suitable for low dissipation and long coherence times.

Superconductivity and Transition Temperature

Normally,  they works extremely low temperature and/or extremely high pressure. Most superconductors are materials that have been cooled to a little above absolute zero. The temperature at which a material becomes a superconductor is called its transition temperature or critical temperature (Tc). An important characteristic of a superconductor is that its normal resistance is restored if a sufficiently large magnetic field is applied.

Above the critical temperature, the net interaction between two electrons is repulsive. Below the critical temperature, though, the overall interaction between two electrons becomes very slightly attractive.

A room-temperature superconductor imply a superconductor having a critical temperature T_c around 300 K.

Superconductive Materials and Critical Temperatures:

The four classes of superconductive materials are: Hydrogen-based superconductor, Copper-oxide superconductors, Iron-based superconductors and Metallic low-temperature superconductors.

Superconductors are classified into Type I and Type II materials. Type I materials show at least some conductivity at ambient temperature and include mostly pure metals and metalloids. They have low critical temperatures, typically between 0 and 10 K (-273°C and -263°C respectively). Copper, silver, and gold are three of the best metallic conductors but are not superconductive. While lead is capable of superconductivity. Most Type II materials are metallic compounds or alloys. They are capable of superconductivity at much higher critical temperatures. They have critical temperatures within the 10-130 K range.

Superconductivity at Room Temperature Recent Research

Up until now, no material has been found conduct current with no resistance at room temperature. However, researchers are looking for new alloys and various combinations of gold, silver, copper, platinum and iron for room temperature superconductivity. Some of their properties can be attributed to the way electrons are arranged.

Researchers have experimented around with carbon-based qubits for some years now, with graphene – a single-layer sheet of carbon atoms – and nanotubes made of rolled graphene promising candidates for room temperature qubits. But carbon nanospheres – tiny balls of carbon a few billionths of a metre wide – weren’t so well-studied.

Electron-phonon coupling in twisted bilayer graphene (TBG), which was recently experimentally observed to exhibit superconductivity.  Twisted bilayer graphene is a precisely tunable, purely carbon-based, two-dimensional superconductor. TBG, was earlier reported to exhibit granular superconductivity with a Tc up to 100K.

 

Metals are colored because the absorption and re-emission of light are dependent on wavelength. Gold and copper have low reflectivity at short wavelengths, and yellow and red are preferentially reflected, as the color here suggests. Silver has good reflectivity that does not vary with wavelength and therefore appears very close to white.

Scientists are looking for the exact relationships between the colors of the metals and superconductivity. Silver, gold and copper have similar electron configurations, but we perceive them as having quite distinct colors.  Electrons absorb energy from incident light, and are excited from lower energy levels to higher, vacant energy levels. The excited electrons can then return to the lower energies and emit the difference of energy as a photon.

Recently  Thapa and Pandey,  declared the emergence of new superconductivity material in an Au-Ag based material at ambient temperature and pressure conditions.  They claimed that they observed superconductivity in nano-sized films and pellets made of silver nanoparticles embedded in a gold matrix. Superconductivity was observed at below 236 K (-37 oC) at ambient pressures. The resistance observed is very low — 10-4 ohms — but not zero. In 2001, the prominent German physicist Jan Hendrik Schön published a paper in Nature in which he claimed to have created a molecular-scale transistor. Like Pandey and Thapa’s superconductivity at room temperature. If it is true, it is an excellent achievement and quantum jump for superconductivity. If not, then we need to look all together in new perspective.

Conclusion:

Quantum computer with superconductivity at room temperature is going to change the directions of artificial intelligence. Superconductivity at room temperature is a promising technology for solving hard problems in quantum computing and a daunting challenge for those working to develop that technology. A proper room temperature superconductor may be a long way to go. However, it is interesting to see, the mode of discovery that is going on in this field. As it has huge impact on Quantum Computing and other allied fields,  an increasing amount of resources are necessary to conduct real research on developing true superconductivity at room temperature.

References:

1. Ray, Amit. “Spin-orbit Coupling Qubits for Quantum Computing and AI.” Compassionate AI, vol. 3, no. 8, 20 August 2018, pp. 60-62, Compassionate AI Lab, https://amitray.com/spin-orbit-coupling-qubits-for-quantum-computing-with-ai/.
2. Ray, Amit. “Roadmap for 1000 Qubits Fault-tolerant Quantum Computers.” Compassionate AI, vol. 1, no. 3, 15 March 2019, pp. 45-47, Compassionate AI Lab, https://amitray.com/roadmap-for-1000-qubits-fault-tolerant-quantum-computers/.
3. Ray, Amit. “Quantum Computing Algorithms for Artificial Intelligence.” Compassionate AI, vol. 3, no. 8, 22 August 2018, pp. 66-68, Compassionate AI Lab, https://amitray.com/quantum-computing-algorithms-for-artificial-intelligence/.
4. Ray, Amit. “Quantum Computing with Many World Interpretation Scopes and Challenges.” Compassionate AI, vol. 1, no. 1, 30 January 2019, pp. 90-92, Compassionate AI Lab, https://amitray.com/quantum-computing-with-many-world-interpretation-scopes-and-challenges/.
5. Ray, Amit. “Roadmap for 1000 Qubits Fault-tolerant Quantum Computers.” Compassionate AI, vol. 1, no. 3, 15 March 2019, pp. 45-47, Compassionate AI Lab, https://amitray.com/roadmap-for-1000-qubits-fault-tolerant-quantum-computers/.
6. Ray, Amit. “Quantum Machine Learning The 10 Key Properties.” Compassionate AI, vol. 2, no. 6, 12 June 2019, pp. 36-38, Compassionate AI Lab, https://amitray.com/the-10-ms-of-quantum-machine-learning/.
7. Ray, Amit. “Quantum Computer with Superconductivity at Room Temperature.” Compassionate AI, vol. 3, no. 8, 25 August 2018, pp. 75-77, Compassionate AI Lab, https://amitray.com/quantum-computing-with-superconductivity-at-room-temperature/.
8. Ray, Amit. “Brain-Computer Interface and Compassionate Artificial Intelligence.” Compassionate AI, vol. 2, no. 5, 1 May 2018, pp. 3-5, Compassionate AI Lab, https://amitray.com/brain-computer-interface-compassionate-ai/.
9. Mankowsky, R., Subedi, A., Först, M. et al. Nonlinear lattice dynamics as a basis for enhanced superconductivity in YBa₂Cu₃O_6.5. Nature 516, 71–73 (2014). https://doi.org/10.1038/nature13875.
10. “Superconductivity Without Cooling.” Phys.org, 1 Dec. 2014, https://phys.org/news/2014-12-superconductivity-cooling.html.
11. Thapa, Dev Kumar, et al. “Coexistence of diamagnetism and vanishingly small electrical resistance at ambient temperature and pressure in nanostructures.” arXiv preprint arXiv:1807.08572 (2018).
12. Wang, F., et al. “Room-temperature storage of quantum entanglement using decoherence-free subspace in a solid-state spin system.” Physical Review B 96.13 (2017): 134314.

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