An emerging technology, quantum computing utilizes the laws of quantum mechanisms to solve complex problems that are beyond the capacity of traditional computers.
These quantum computers store information in qubits (or quantum bits). Unlike classical bits, these qubits can exist beyond a binary state of 0 and 1 and, as such, can perform computations much quicker.
Moreover, these qubits come in different forms, including trapped-ion qubits, which use charged ions or atoms; photonic qubits, which use light particles; and superconducting qubits, which are a circuit loop with an electrical current traveling around them.
Part of ‘solid-state’ quantum computation, superconducting qubits were first demonstrated in 1999. Since then, they have evolved into one of the primary forms of qubit technology, offering benefits such as reduced energy dissipation, low resistance, decreased decoherence, scalable quantum circuits, high-speed qubit operation, stable qubit states, high-fidelity qubit control, and error correction.
Over the past decade, superconducting quantum computing has become a popular option for building functional quantum computers, and ongoing research is bringing us closer to making them a reality.
Recent Breakthroughs in Superconductor Materials
Just this week, a team of researchers published a study in Science Advances on the development of a new superconductor material for quantum computing.
The new superconductor material is a candidate for a “topological superconductor,” which is a type that uses a hole or an electron’s delocalized state to carry quantum information and process data.
Physicist Peng Wei from the University of California led a team of researchers who combined trigonal tellurium, a non-magnetic material that cannot be superimposed on its mirror image, with a surface state superconductor generated on the surface of a thin film of gold.
This combination created a 2D interface superconductor with enhanced spin polarization, allowing the excitations to potentially be used to create a stable spin qubit. This groundbreaking superconductor material has the potential to revolutionize the scalability and reliability of quantum computing components.
“By creating a very clean interface between the chiral material and gold, we developed a two-dimensional interface superconductor. The interface superconductor is unique as it lives in an environment where the energy of the spin is six times more enhanced than those in conventional superconductors.”
– Wei, an associate professor of physics and astronomy
Under a magnetic field, the material was further seen making a transition, which suggests its usage as a triplet superconductor, which could lead to more robust quantum computing components. It basically became more robust at a high magnetic field than at a low magnetic field.
Furthermore, by using non-magnetic materials for cleaner interfaces, this new technology also naturally suppresses the sources of decoherence, which is a challenge in quantum computing.
The researchers also demonstrated the superconductor’s ability to be made into top-quality low-loss microwave resonators, which are critical components of quantum computing. As such, this can lead to low-loss superconducting qubits.
Given that reducing decoherence or loss of quantum information in a qubit system is the biggest challenge in quantum computing, this research can help develop more scalable and reliable quantum computing components. According to Wei:
“We achieved this using materials that are one order of magnitude thinner than those typically used in the quantum computing industry.”
These microwave resonators have a quality factor reaching 1 million.
A week before this, a UCLA-led team also published a study presenting new material that shows promise for quantum computing.
The material retained its superconducting properties under much higher-than-usual magnetic fields and exhibited the superconducting diode effect. This effect, which allows more current to flow in one direction, is typically seen in chiral superconductors and is scarcely seen in traditional superconductors.
To induce the chiral behavior in a conventional superconductor, the researchers created a chiral molecular layer and a layered structure with 2D material tantalum disulfide (TaS2).
This study showcased the potential to enhance the efficiency and stability of quantum computing and make conventional electronics faster and more energy-efficient.
Innovations in Qubit Control and Scalability
With quantum computers having the capability to “drastically change the world,” there has been a race worldwide to build a practical quantum computer.
However, one of the biggest challenges obstructing the growth of quantum computers is scalability, which means that large enough computers can tackle real-life problems. To have a quantum computer that can tackle useful problems, we either need more qubits or a reliable way to reduce errors introduced during calculations.
So, researchers in Japan took to tackling the problem by increasing the manageable number of qubits and decreasing the required number of qubits.
A couple of months ago, the researchers successfully demonstrated a superconducting circuit that can control many qubits at low temperatures.
In this experiment, a superconducting circuit was shown to control multiple qubits through just one cable using microwave multiplexing. The circuit has the potential to improve the microwave signals’ density per cable by about 1,000x. This achievement can substantially boost the number of controllable qubits and contribute to the development of large-scale quantum computers.
To cut down the hardware required to go in the middle of qubits and room-temperature electronics, an innovative ‘cryo-electronics’ was developed. ‘Cryo-electronics’ is electronics for qubit control and readout that operate at cryogenic temperatures near the qubits.
Cryo-electronics have also been demonstrated to function at high-speed clock frequencies at four degrees above absolute zero. Now, the focus is on reducing energy consumption to minimize the heat generated next to the qubits.
Yet another focus of Japanese researchers is finding ways to correct processing errors. Amidst this, researchers from Princeton University developed a fabrication technique for error-free quantum computing.
In this research, scientists created a superconducting layer on top of a topological insulator, tungsten ditelluride (WTe2). The technique used a ‘seed’ of deposited metal (palladium) over the surface of the insulator to form a new crystalline structure, Pd7WTe2, which exhibited zero resistance.
The atom-spreading technique successfully works with a variety of ingredients, including molybdenum ditelluride (MoTe2).
While further tests are required to determine if it’s a topological superconductor, the researchers believe new superconductors can be created through their general method.
Addressing Decoherence and Improving Performance
Another breakthrough in quantum computing came earlier this year when researchers introduced a new approach to superconducting circuits. This approach has the potential to significantly extend the runtime of a quantum computer.
As we have noted, the continuous operation of such a computer gets interrupted due to how easily the quantum state of a qubit can be destabilized. This is called decoherence and leads to errors in computations. This happens because of interactions with other qubits and their environment.
And because superconducting qubits enable switching between different states in the shortest amount of time, they are the focus of growing research. But while they can enhance switching time, they are also more susceptible to decoherence in as little time as milliseconds.
So, an international group of researchers proposed a Josephson junction design, which is termed “flowermon.” This design uses two one-atom-thick cuprate flakes, a superconducting material based on copper.
“The flowermon modernizes the old idea of using unconventional superconductors for protected quantum circuits and combines it with new fabrication techniques and a new understanding of superconducting circuit coherence.”
– Uri Vool, a physicist at the Max Planck Institute for Chemical Physics of Solids in Germany
According to the team’s calculations, their design can reduce noise and, in turn, increase the coherence time of qubits by orders of magnitude. However, it was purely theoretical, and the team plans to use its results to optimize superconducting qubits next.
To tackle the performance of quantum computers, last year, a team of researchers from the University of Minnesota Twin Cities also developed a tunable superconducting diode that can not only help scale up quantum computers but also improve artificial intelligence systems.
A diode is a device that allows the flow of current in one direction. While usually made with semiconductors, researchers have been exploring making diodes with superconductors, which allow energy transfer without losing any power along the way.
The senior research author Vlad Pribiag, who’s an associate professor at the University of Minnesota School of Physics and Astronomy, noted:
“We want to make computers more powerful, but there are some hard limits we are going to hit soon with our current materials and fabrication methods.”
The biggest challenge to enhancing computing power is dissipating energy, so the team chose to use superconducting technologies.
The superconducting diode device was built using three Josephson junctions. While made by sandwiching pieces of non-superconducting material in the middle of superconductors, the researchers here had the superconductors connected with layers of semiconductors.
This unique design allowed the researchers to control the device’s behavior using voltage. It can also process multiple electrical signals at a time, unlike the usual diodes, which can only handle one input and output each. These features can see the superconducting diode even being used in brain-inspired neuromorphic computing.
In neuromorphic computing, electrical circuits are designed to copy how neurons work in the human brain to enhance performance.
According to Mohit Gupta, the paper’s first author, this new superconducting diode is more energy efficient than other superconducting diodes. More specifically, for the first time, it comes with a series of gates to control the flow of energy. This feature hasn’t been incorporated into a superconducting diode before, but this study has “shown that you can add gates and apply electric fields to tune this effect.”
Moreover, the material used in this research was more industry-friendly and able to deliver new functionalities.
The technique used in this study can further be utilized with any superconductor, which makes it highly flexible and compatible with industry applications. These qualities can help scale up the development of quantum computers for wider use.
“Right now, all the quantum computing machines out there are very basic relative to the needs of real-world applications. Scaling up is necessary in order to have a computer that’s powerful enough to tackle useful, complex problems.”
– Pribiag
This holds special significance today as AI usage grows substantially. This has led to people researching algorithms for computers or AI machines that can surpass classical computers’ performance. This study, Pribiag noted, is developing the hardware to enable quantum computers to implement these algorithms.
The research was funded primarily by the United States Department of Energy with partial support from the National Science Foundation and Microsoft Research.
Shrinking Qubits With 2D Materials Without Affecting Performance
Continuing research and development have led to scientists building superconducting qubits that are far smaller than usual qubits. These superconducting qubits were built using 2D materials.
In order to surpass the speed and capacity of classical computers, quantum computers’ qubits need to be on the same wavelength. To achieve this, researchers have to usually sacrifice the size of these qubits, which even today are measured in millimeters unlike their classical counterparts, whose transistors have shrunken to nanometer.
To reduce the size of qubits so that they don’t have a large physical footprint while maintaining their performance, James Hone, a Wang Fong-Jen Professor of Mechanical Engineering at Columbia University, displayed a really small superconducting qubit capacitor.
Previously, engineers used planar capacitors to build qubit chips. Here, charged plates are set side by side, and while they can be stacked to save space, that would interfere with the qubit information storage.
So, Hone’s PhD students Anjaly Rajendra and Abhinandan Antony sandwiched an insulating layer of boron nitride between two charged plates of superconducting niobium diselenide. Just one atom thick, these layers are held together by van der Waals forces, a weak interaction between electrostatic forces.
The capacitors were then combined with aluminum circuits to create a chip. This chip had two qubits and was only 35 nanometers thick, 1,000 times smaller than those produced using conventional approaches.
When cooled down, the qubits got the same wavelength. They were also observed to become entangled and act as a single unit. This quantum coherence, though only short-lived (a little over one microsecond), means the quantum state of the qubit can be manipulated and read out via electrical pulses. According to Hone:
“We now know that 2D materials may hold the key to making quantum computers possible. It is still very early days, but findings like these will spur researchers worldwide to consider novel applications of 2D materials. We hope to see a lot more work in this direction going forward.”
Thanks to their unique structure, two-dimensional (2D) quantum materials have marked a significant breakthrough in materials science. Unlike 3D materials, 2D quantum materials are just one or a few atoms thick, and electrons can move in all three directions.
Some popular 2D materials include Silicene, Graphene, Germanene, Stanene, Phosphorene, Transition Metal Dichalcogenides (TMDCs), and Hexagonal Boron Nitride (h-BN).
While these materials offer diverse properties and potential for transformative technological applications, they face challenges in terms of synthesis, integration, and scalability that need to be overcome before their full potential can be realized.
Key Companies Leading the Quantum Computing Revolution
Now, let’s take a look at some prominent companies that are involved in superconductors and quantum computing:
#1. Alphabet (Google)
Alphabet is heavily invested in quantum computing research through its subsidiary Google Quantum AI. The division has created a superconducting quantum processor called Sycamore, which, back in 2019, was able to complete a calculation in 200 seconds that otherwise would have taken 10,000 years for even a powerful supercomputer. Since then, the Sycamore quantum processor has grown substantially and now holds 70 qubits, making it 241 million times more robust than its previous model.
The tech giant has a market cap of $2.06 trillion, and its shares (GOOGL:NASDAQ) trade at $165.68, up 18.56% YTD. For Q2 2024, Alphabet reported a 28.6% increase in its net income to $23.6bln, while total revenue grew 14% to $84.74bln. The Google parent also announced a cash dividend of $0.20 per share.
#2. NVIDIA Corporation
NVIDIA has been exploring quantum computing and superconductors through partnerships and collaborations. In March this year, the company announced the acceleration of its quantum computing efforts at national supercomputing sites in Germany, Japan, and Poland with the open-source NVIDIA CUDA-Q™ platform.
The AI darling of the market, NVIDIA stocks have been having a great time this year, as evidenced by their 161.24% spike in 2024 so far. This upside has NVDA shares trading at $129.45, putting the company’s market cap at $3.188 trillion. The chipmaker reported a record Q1 of 2024, with its revenue coming in at $22.1bln.
Conclusion
So, researchers, organizations, and companies around the world are working on advancing quantum computing, which excels at complex problem-solving. The focus on superconducting technology, in particular, is helping drive significant progress and bringing us closer to realizing this transformative technology’s full potential.
Click here to learn about the current state of quantum computing.
