While quantum computers have seen massive improvements in their scale, quality and speed in recent years, reducing quantum errors, the continuous path from current quantum hardware to future fault-tolerant quantum computers, “seems to be missing from the story,” according to IBM. .
In newly published research, the company notes that the first step and ultimate goal is to build a large fault-tolerant quantum processor “before one of the quantum algorithms with proven superpolynomial acceleration can be implemented.”
Recent advances in techniques commonly referred to as quantum error mitigation provide a smoother path to this goal.
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“Along this path, advances in qubit coherence, gate fidelity and speed translate immediately into measurable benefits in computation, similar to the steady progress historically observed with classical computers,” the company wrote in a statement. blog on tuesday. “The ultimate litmus test for practical quantum computers is to provide an advantage over classical approaches to a useful problem. Such an advantage can take many forms, the most prominent being a substantial improvement in the runtime of a quantum algorithm over the best classical approaches.”
This requires the algorithm to have an efficient representation as quantum circuits, for which two questions must be answered. The first is figuring out which problems can be assigned to quantum circuits that have solutions that are better than classical approximations.
The second is to determine how to get reliable results for these circuits on quantum hardware with a faster runtime.
To answer the first question, IBM said it is working with the community and industry experts to find problems solvable with quantum circuits that are known to be difficult to simulate classically. It is already doing this through its IBM Quantum Network, which includes Fortune 500 companies, academic institutions, national entities, start-ups and the Qiskit community to explore the problem space of quantum circuits to drive real application and value.
Answering the second question in practice is more challenging. Today’s quantum hardware is subject to several sources of noise, the most well-known of which, according to IBM, are qubit decoherence, individual gate errors, and measurement errors.
“These errors limit the depth of the quantum circuit we can implement,” IBM said. “But even for shallow circuits, noise can lead to erroneous estimates. Fortunately, quantum error mitigation provides a set of tools and methods that allow us to evaluate accurate expectation values of low-depth, noisy quantum circuits even before the introduction of fault tolerance.”
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Probabilistic Error Cancellation is a “secret sauce technique” used to effectively invert noisy circuits to get error-free results, even though the circuits themselves are noisy.
In 2021 IBM unveiled the 127 qubit Eagle processorthe first quantum processor capable of quantum circuits that cannot be simulated classically.
Detailed in the comprehensive quantum roadmap unveiled in May, the number of qubits within its systems is on track to achieve 4,000+ in 2023. The milestones mapped to increase the power, quality, and accessibility of quantum hardware and software serve as the foundation for quantum advantage.
Even after larger processors are unveiled, the company continues to improve their performance at its research headquarters in Yorktown Heights, NY.
One of these improvements is in the consistency of the qubits. IBM said it has more than doubled the coherence times on its 65-qubit chips since they were unveiled in 2020, and each improvement further reduces errors in the quantum circuitry.
These factors interact exponentially and amplify each other’s effects.
“Taken together, all of the above means ever-larger quantum computers with ever-decreasing error rates,” IBM wrote. “And this puts us on a trajectory where we can deliver quantum computers that can outperform classical computers — perform calculations faster, better, and more efficiently.”
The company also noted that these ideas go beyond theory and officials have already started demonstrating the effectiveness of error mitigation on large processors.
The path to quantum advantage will be driven by improvements in the quality and speed of quantum systems as their scale grows to tackle increasingly complex circuits, IBM said. It has already introduced a metric to quantify the speed of quantum systems – CLOPs – and demonstrated a 120x reduction in the run time of a molecular simulation.
“The coherence times of our transmon qubits exceeded 1 ms, an incredible milestone for superconducting qubit technology,” IBM said. seen improvement in coherence, which further allows for higher reliability gates.”
In the latest Falcon r10 processor, IBM Prague, two-qubit port errors dipped below 0.1%, which IBM says was “another first for superconducting quantum technology, allowing this processor to demonstrate two steps in Quantum Volume of 256 and 512.” .”