Quantum progress: qubit controller enters cryogenic chamber

The qubit controller developed by SEEQC can operate at ultra-low temperatures in the cryogenic chamber where the qubits themselves are (photo: SEEQC)

The superconducting qubits used by quantum computer developers have one serious drawback. The electronics that control the qubits, in the form of simple digital controllers, cannot be heavily cooled and must be kept separate from the qubits, making such implementations extremely complex and cumbersome. However, an American company has created low-temperature controllers that can solve this problem.

The startup SEEQC (Superconducting Energy Efficient Quantum Computing) is developing chips called Single Flux Quantum (SFQ), Reuters reported. They are able to perform all the basic functions of a quantum qubit controller at the same cryogenic temperature as the qubits themselves, which is about 20 mK. This means that the controller can work together with the qubits in the same cryogenic chamber, greatly simplifying the architecture of quantum systems that today look like huge cabinets taller than human height.

The SEEQC developers intend to promote hybrid computers – a combination of quantum and classical systems, and this requires electronics that can withstand ultra-low temperatures. But controllers alone won’t be enough. Cryogenic circuits are needed that digitize the wave data read by the qubits. SEEQC develops just such logic, but does not rely on classic transistors.

For now, no further details are known about the development, but it can be assumed that the company uses a junction with the Josephson effect in the role of a “cryogenic transistor”. The essence of the effect is that under certain conditions the dielectric between two superconductors can begin to pass current. SEEQC has previously been involved in experiments with such elements. In particular, the company has developed cryogenic memory with Josephson junctions for quantum and conventional computers.

According to the company, the SFQ chips exchange data wirelessly and are compatible with all types of superconducting qubits and even spin qubits. Multiplexing is used to simplify the architecture. A solution for driving 8 qubits using 2 wires has already been tested. The 64-qubit control version will soon be available for extensive testing.

Meanwhile, Intel is following the same path. The company is developing the Horse Ridge family of cryogenic controllers for controlling superconducting and spin qubits. So far, Intel cannot boast of controller operation at temperatures close to absolute zero. Its chips run at 4K and can’t be placed near qubits. But Intel’s technology has one definite advantage – Horse Ridge controllers are manufactured with conventional silicon transistors, which are much easier to work with.

Both Intel and SEEQC are moving in the same direction – they want to create an electronic qubit controller that resides in the same cryogenic environment as the quantum information carriers. This will significantly reduce the time to create a sufficiently powerful quantum computer with practical application.