Quantum device with multiplexed electrometer output signals
A quantum device includes several spin qubits arranged as a matrix and each comprising a quantum dot; several electrometers each electrostatically coupled to a potential well of one of the quantum dots; and circuits for applying an excitation signal to an input electrode of each electrometer. The circuits are configured such that a value of the frequency, phase or maximum amplitude of each excitation signal is different from that of the other excitation signals, and the circuits apply a same excitation signal on electrometers coupled to a same row of qubits. The device also includes a transimpedance amplifier having an input coupled to output electrodes of the electrometers and a demultiplexing circuit including an input electrically coupled to an output of the transimpedance amplifier and configured to demultiplex the output signals to be delivered by the electrometers.
1. A quantum device comprising:
several spin qubits each comprising at least one quantum dot, the qubits being arranged by forming a matrix of qubits;
several electrometers each electrostatically coupled to a potential well of the quantum dot of one of the spin qubits;
circuits configured to apply at least one AC excitation signal to at least one input electrode of each of the electrometers, configured such that a value of at least one parameter from a frequency, phase and maximum amplitude of each of the excitation signals is different from that of the other excitation signals; each circuit being configured to apply at least one AC excitation signal being configured to apply a same excitation signal to input electrodes of electrometers coupled to qubits arranged on a same row of the matrix of qubits;
a transimpedance amplifier comprising an input electrically coupled to output electrodes, distinct from the input electrodes, of at least two of the electrometers to which output signals are to be delivered; and
a demultiplexing circuit including an input electrically coupled to an output of the transimpedance amplifier, and configured to demultiplex the output signals to be delivered by the electrometers.
2. The quantum device according to claim 1 , further including a cryostat including a chamber configured to be maintained at a temperature less than or equal to 4K and in which at least the spin qubits, the electrometers and the transimpedance amplifier are arranged.
3. The quantum device according to claim 1 , further including circuits for biasing the electrometers configured to apply DC bias voltages to the electrometers.
4. The quantum device according to claim 3 , wherein the circuits for biasing the electrometers comprise:
a digital-to-analogue converter, configured to receive as an input at least one digital signal coding values of bias voltages of the electrometers;
a demultiplexer comprising an input electrically coupled to an output of the digital-to-analogue converter, and several outputs to which the bias voltages of the electrometers are to be delivered; and
sample-and-hold devices each comprising an input electrically coupled to an output of the demultiplexer.
5. The quantum device according to claim 1 , wherein the electrometers correspond to single electron transistors and/or quantum point contacts.
6. The quantum device according to claim 5 , wherein:
when the electrometers correspond to single electron transistors, the circuits for applying excitation signals are coupled to a gate or source or drain of each of the single electron transistors, or are coupled to the gate and source of each of the single electron transistors, or are coupled to the gate and drain of each of the single electron transistors; and
when the electrometers correspond to quantum point contacts, the circuits for applying excitation signals are coupled to a first of two electrodes of each of the quantum point contacts.
7. The quantum device according to claim 3 , wherein the electrometers correspond to single electron transistors and/or quantum point contacts, and wherein the circuits for biasing the electrometers are configured to:
when the electrometers correspond to single electron transistors, apply DC bias voltages to a gate and a drain of each of the single electron transistors when the circuits for applying excitation signals are coupled to at least one of the gate and the drain of each of the single electron transistors, or to a gate and a source of each of the single electron transistors when the circuits for applying excitation signals are coupled to at least one of the gate and the source of each of the single electron transistors; and
when the electrometers are quantum point contacts, apply DC bias voltages to a first of both electrodes of each of the quantum point contacts.
8. The quantum device according to claim 1 , wherein the electrometers are arranged by forming a matrix of electrometers arranged facing the matrix of qubits such that the quantum dot of each of the qubits is electrostatically coupled to a quantum dot of one of the electrometers.
9. The quantum device according to claim 1 , wherein the output electrodes of electrometers coupled to qubits arranged on a same column of the matrix of qubits are coupled to the input of a same transimpedance amplifier.
10. The quantum device according to claim 1 , wherein:
each of the circuits for applying at least one excitation signal, forms a first circuit for applying at least one first excitation signal configured to apply a same first excitation signal to first input electrodes of electrometers coupled to qubits arranged on a same row of the matrix of qubits;
the quantum device further includes second circuits for applying at least one second excitation signal, each configured to apply a same second excitation signal to second input electrodes of electrometers coupled to qubits arranged on a same column of the matrix of qubits;
the first and second application circuits are configured such that a value of at least one parameter from a frequency, phase and maximum amplitude of each of the first and second excitation signals is different from that of the other excitation signals; and
the input of the transimpedance amplifier is electrically coupled to an output electrode of each of the electrometers.
11. The quantum device according to claim 1 , further comprising:
a digitising circuit comprising inputs coupled to outputs of the demultiplexing circuit and configured to digitise the output signals to be delivered from the demultiplexing circuit, or
an analogue-to-digital converter interposed between the input of the demultiplexing circuit and the output of the transimpedance amplifier.
12. The quantum device according to claim 11 , wherein, when the quantum device includes the digitising circuit:
the demultiplexing circuit includes several mixers each comprising a first input electrically coupled to the output of the transimpedance amplifier and a second input configured to receive one of the excitation signals; and
the digitising circuit includes several integrators each comprising an input electrically coupled to an output of one of the mixers, and several comparators each comprising an input electrically coupled to an output of one of the integrators.
13. The quantum device according to claim 2 , further comprising:
a digitising circuit comprising inputs coupled to outputs of the demultiplexing circuit and configured to digitise the output signals to be delivered from the demultiplexing circuit, or
an analogue-to-digital converter interposed between the input of the demultiplexing circuit and the output of the transimpedance amplifier;
wherein the circuits for applying excitation signals, the demultiplexing circuits, and the digitising circuits are arranged in the cryostat chamber.
14. The quantum device according to claim 13 , wherein:
the cryostat chamber includes a first part configured to be maintained at a temperature of less than 1K and a second part configured to be maintained at a temperature between 1K and 4K;
the spin qubits, electrometers and transimpedance amplifier are arranged in the first part of the cryostat chamber; and
the circuits for applying excitation signals, demultiplexing circuit and digitising circuit are arranged in the second part of the cryostat chamber.
15. A quantum device comprising:
several spin qubits each comprising at least one quantum dot;
several electrometers each electrostatically coupled to a potential well of the quantum dot of one of the spin qubits;
circuits for applying at least one excitation signal to at least one input electrode of each of the electrometers, configured such that a value of at least one parameter from a frequency, phase and maximum amplitude of each of the excitation signals is different from that of the other excitation signals;
a transimpedance amplifier comprising an input electrically coupled to output electrodes, distinct from the input electrodes, of at least two of the electrometers to which output signals are to be delivered; and
a demultiplexing circuit including an input electrically coupled to an output of the transimpedance amplifier, and configured to demultiplex the output signals to be delivered by the electrometers.
16. The quantum device according to claim 15 , wherein a variation in conductance of each electrometer represents a state of a corresponding spin qubit.
17. The quantum device according to claim 15 , wherein the excitation signal applied at the input of each electrometer corresponds to a signal that modifies a current generated at the output by said electrometer, the current flowing out of each electrometer corresponding to the output signal delivered to the output electrode of said electrometer.