Quantum scientists worldwide are working to improve quantum computers, making them more reliable and powerful. The German start-up eleQtron sells groundbreaking quantum computers that use microwave radiation instead of lasers to control individual trapped ion qubits, delivering a simpler design with greatly reduced cooling and power consumption. This significant advancement is made possible by AWGs from Spectrum Instrumentation, which utilise advanced Direct Digital Synthesis (DDS) technology to support up to 20 sine wave carriers per output, thereby enabling the execution of quantum operations.
The company eleQtron, a spin-off from the University of Siegen, recently delivered a quantum computer that implements its patented MAGIC (MAgnetic Gradient Induced Coupling) quantum processors. MAGIC differentiates from other quantum processor designs by employing microwave radiation, instead of lasers, to control and manipulate the qubits.
Laser ablation is used initially in a high vacuum to create a string of Ytterbium (171Yb+) ions. This process can build a string of up to 30 ions in a single register, each one functioning as a qubit. Key to implementing quantum algorithms is the use of a magnetic field and an oscillating electric field to generate a Paul trap (quadrapole ion trap). Many designs employ a laser at this stage to control and manipulate the qubits, preparing them to execute quantum gates. Such lasers, however, must be incredibly accurate in targeting each ion individually and have high power requirements.
By comparison, microwaves are technically simpler and need around one-fifth of the power. A high-frequency oscillator source and the output of the company’s DDS card are combined using a single sideband (SSB) mixer, generating a signal around 12.64GHz. Thanks to the Zeeman effect resulting from the magnetic field, each ion can be ‘addressed’ by modulating the signal in deltas of 3MHz to 5MHz, which offers low crosstalk and integrates nicely with chip-based ion traps. The DDS card generates the multi-tone signal that is needed to implement individual control and manipulation of the qubits.
The eleQtron scientists reached out to the company when they hit the limits of their existing AWG hardware. The signals generated need to be modified in amplitude, phase offset, pulse length, and frequency to control each qubit correctly. This helps achieve the desired Rabi frequency that determines the speed of quantum operations. But such needs place considerable demands on the AWG.
The eleQtron team was recommended the M4i.66xx-series of 16-bit AWGs, a well-known instrument line in the community of quantum researchers worldwide. These PCIe cards can offer one, two, or four synchronous channels with up to 1.25GS/s output rate, and a large onboard memory that can be segmented to replay different waveforms. With Spectrum’s optimised drivers, data transfer rates of 2.8GB/s are attainable, and up to eight cards can be synchronised, if required. With the additional DDS firmware, the outputs allow up to 20 sine wave cores on one channel. Each DDS core can be programmed for frequency, amplitude, phase, frequency slope and amplitude slope with just a few commands, which leads to ultrafast changes on the sine wave cores with a resolution of 6.4ns. This helps to address more qubits and enables the flexibility in quantum processor design, which is needed to implement more complex quantum circuits. For the eleQtron team, the DDS solution was the key to their concept. They also reported about the outstanding support they got from Spectrum, from the quality of the documentation to the rapid response by the design engineers themselves.