IBM has described a quantum computing roadmap that incorporates a number of advancements in future machines that include innovations at the chip, electrical, mechanical, and software technology levels. The goal is to not only improvement the number of qubits in the machines, but also improve the qubit quality metrics so that meaningful error correction algorithms can be implemented in future machines.
Like many engineering projects in technology companies, IBM is using codenames to identify the developments and has decided to use names of birds for this one. The recently announced Hummingbird development came online on September 1, 2020 and is based upon a topology that IBM calls a heavy hexagon lattice that IBM believes provides a balance between connectivity and reduction of crosstalk error. They are planning a cadence of having a new machine every year or so with each one having about 2-3 times more qubits than before. So Hummingbird will be followed in 2021 with Eagle at 127 qubits, Osprey in 2022 at 433 qubits, and Condor in 2023 with 1121 qubits.
To achieve this pace, IBM is planning on pushing its technologies in several different ways including the following:
- The Hummingbird, Eagle, and Osprey machines will use packaging and a dilution refrigerator similar to the IBM System 1 that IBM previously announced. However, for the 1121 qubit Condor, they will have a new family with a new infrastructure. IBM is developing their own super dilution refrigerator codenamed Goldeneye (aka Superfridge) sized at 10 x 6 feet for even larger future machines.
- More qubits means more controls and control wiring. For the Hummingbird, IBM has implemented an 8:1 readout multiplexing to reduce the number of wires going to the classical computer for readouts. They are also planning to reduce latency in the control electronics in future systems and provide the ability to conditionally control qubits in real time based upon classical conditions. Longer term, some of the control electronics may possibly be moved inside the fridge and be placed next to the qubit chips on a quantum motherboard to ease the wiring and control.
- With their chip technology IBM will incorporate through silicon vias (TSVs) and multi-level wiring. This will help protect the qubits from signals which can degrade coherence times while providing more fan-out for the higher number of control lines. They will also use Cryi-flex cables to replace the individual coax cables.
- To reach a million qubit level, IBM is also planning to implement stacking multiple quantum motherboards inside the same dilution refrigerator. This can be viewed similar to the way modern classical microprocessors use a multicore technology to have multiple processors inside a single package.
- IBM is also developing technology to use optical networking to connect multiple systems to each other. However, these networks won’t be standard classical optical networks, but will effectively be a mini quantum internet and will be exchanging entangled photons with each other. So like a classical computer data center that uses multicore chips in a multi-processor arrangement to provide high performance, IBM’s vision of a future quantum data center be somewhat analogous.
- And finally, advancements will be needed in the software in order to keep up with the changing hardware. In an environment where there are multicore chips in a multiprocessor environment, one of the key challenges will be providing software that can automatically partition a quantum program and assign different pieces to the different processors. This is a complex problem because the qubit-to-qubit connectivity between processors will be much less that the connectivity within a processor. The software will need to be aware of these constraints in order to effectively compile a program that can take advantage of the increased processing power.
For more on IBM’s roadmap, you can view the news release on their web site here.
September 15, 2020