IBM sets quantum bit (qubit) error reduction records

February 29, 2012 — IBM Research (NYSE:IBM) established new records for reducing errors in elementary computations and retaining the integrity of quantum mechanical properties in quantum bits (qubits) for quantum computing. IBM uses superconducting qubits, which are made with established microfabrication techniques developed for silicon semiconductor technology. This manufacturing technology allows for a future scaling up to manufacture thousands or millions of qubits.

Qubits boast unique properties that will allow quantum computers to work on millions of computations simultaneously. Qubits can hold a value of 1 or 0 as well as both values at the same time, described as superposition. A single 250-qubit state contains more bits of information than there are atoms in the universe.  

"It’s time to start creating systems based on this science," said IBM scientist Matthias Steffen, manager of the IBM Research team developing quantum computing systems for real-world problems. To do so, scientists must control or remove quantum decoherence: creation of errors in calculations caused by interference from factors such as heat, electromagnetic radiation, and materials defects. When the time periods over which the qubits retain their quantum mechanical properties are sufficiently long, error correction schemes become effective, making it possible to perform long and complex calculations.

Also read: Silicon semiconductor entanglement realized by quantum computing

IBM experimented with a 3D superconducting qubit, originally designed at Yale University, to extend the amount of time that the qubits retain their quantum states up to 100 microseconds (2-4x beyond previous records). 100 microseconds is just past the minimum threshold to enable effective error correction schemes.

Photo 1. IBM’s 3D qubit device, where a qubit (about 1mm in length) is suspended in the center of the cavity on a small sapphire chip. The cavity is formed by closing the two halves, and measurements are done by passing microwave signals to the connectors. Despite the apparent large feature size (the cavity is about 1.5" wide) for this single qubit demonstration, the team believes it is possible to scale such a system to hundreds or thousands of qubits.

IBM also demonstrated a more traditional 2D qubit device and implemented a 2-qubit logic operation — a controlled-NOT (CNOT) operation. It showed a 95% success rate, enabled in part by the long coherence time of nearly 10 microseconds.

Photo 2. Silicon chip housing 3 qubits. The chip is back-mounted on a PC board and connects to I/O coaxial lines via wire bonds (scale: 8 x 4mm). A larger assembly of such qubits and resonators are envisioned to be used for a scalable architecture.

Quantum computing research efforts now must now include systems integration aspects, such as assessing the classical information processing demands for error correction, I/O issues, feasibility, and costs with scaling, IBM said. IBM envisions a practical quantum computing system as including a classical system intimately connected to the quantum computing hardware. Expertise in communications and packaging technology will be essential at and beyond the level presently practiced in the development of today’s most sophisticated digital computers.  

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