VTT Q5

VTT Q5 is a 5 qubit superconducting quantum computer co-developed and built by IQM and VTT. It uses flux-tunable qubits and couplers which are described in this paper¹.

VTT Q5 in the Lab

Q5’s qubits are arranged in a star-shaped topology, meaning that the central qubit, QB3, is connected to all of the outer qubits, QB1, QB2, QB4. Two-qubit gates can be applied only between the central qubit and the outer qubits.

Q5 Topology

The qubits are pairwise connected with tunable couplers.

Native-gate set

To run arbitrary quantum circuits, a QPU needs to implement a universal gate set. Q5 implements the following gates natively:

• Single-qubit gates: Phased-RX gate (PRX)
• Two-qubit gate: Controlled-Z gate (CZ)

Measurements are natively implemented as single-qubit measurements in the Z basis.

Characteristics

The values below are averaged values. Actual values might differ from day-to-day.

	QB1	QB2	QB3	QB4	QB5
Drive Frequencies [GHz]	4.4	3.9	4.2	4.4	4.4
Readout Frequencies [GHz]	5.3	5.0	6.2	5.9	5.6
T1 time [µs]	35.5	25.7	40.2	41.3	36.0
T2 time [µs]	19.2	17.7	9.12	19.1	22.2
T2 echo time [µs]	45.2	33.1	26.5	47.7	35.0
Single-Qubit Gate Fidelities2 [%]	99.4	99.7	99.7	99.6	99.7
Readout Fidelities [%]	96	95	95	95	95

The coupler characteristics are given below.

	TC-3-1	TC-3-2	TC-3-4	TC-3-5
Two-qubit Gate Fidelities3 [%]	96.4	95.9	94.6	97.5

The PRX gate length and the CZ gate length is 120 [ns] respectively.

Hardware specifics

Q5 uses Zurich Instruments (ZI) devices:

• 2 x HDAWG: Arbitrary waveform generator for generating driving pulses.
• 1 x UHFQA: Quantum analyzer to measure the qubits state.

Known Issues

ZI error

Error: "TimeoutError: A programmable instrument did not stop executing, likely because it missed triggers

This is a known error and limited to Q5 due to Q5 using Zurich Instrument control electronics. The error occurs when using a combination of a large number of shots (1M shots) over 5 qubits.

The current workaround is to either reduce the batch size, or acquire the data by repeating runs of the same batch with lower shot count.

VisaIOError

pyvisa.errors.VisaIOError:
('VI_ERROR_IO (-1073807298): Could not perform operation because of I/O error.',
"asking 'GETN? 1,128' to <SIM928: flux_bias_source>")

This is a known error with the SIM mainframe which provides the flux bias source for Q5’s tunable qubits. This error occurs occasionally and is an issue with this particular instrument. If the issue occurs repeatedly a restart of the instrument may be needed.

Access

• Device URL: https://qx.vtt.fi/api/devices/q5

• Latest Client Libraries:

  Client Library	Package Name	Compatible Version
  Cirq on IQM	cirq-iqm	>= 16.0, < 17.0
  Qiskit on IQM	qiskit-iqm	>= 17.3, < 18.0
  IQM Client	iqm-client	>= 22.3, < 23.0

• Pulse Level: WIP

Footnotes

1. Long-Distance Transmon Coupler with cz-Gate Fidelity above 99.8%, Marxer et al.

2. Calculated via randomized benchmarking

3. CZ gate fidelity calculated via interleaved randomized benchmarking