Semiconductor charge qubit

Description

A single electron is trapped in a double quantum dot. The double quantum dot consists of two quantum dots coupled to each other via a tunnel barrier and the electron can flip back and forth between them. Voltage pulses on the dots can be used to perform quantum operations on the state of the qubit.

Figure

Motivation

A semiconductor system in, e.g., GaAs or Silicon, much like a classical transistor can be used to create solid-state qubits. The charge qubit is the simplest semiconductor qubit. Although it typically suffers from fast decoherence and relaxation, the semiconductor charge qubit demonstrates first, that artificial atoms can be formed out of semiconductors, and two, that all electrical control of a qubit is possible.

References

• https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.91.226804
• T. Fujisawa et al., Physica E 21, 1046 (2004)
• https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.105.246804

Linked Papers

• petersson-2010-semiconductor-charge

Related Entries

• loss-divincenzo-qubit

Seed Metadata

• date_published: 2003-11-26

Physics

Qubit encoded in the position of a single electron in a double quantum dot: $|L⟩$ (left dot) and $|R⟩$ (right dot). The Hamiltonian:

$H=\frac{ϵ}{2}{\sigma }_z+t_c{\sigma }_x$

where $ϵ$ is the detuning (gate-voltage controlled) and $t_c$ is the tunnel coupling. At zero detuning ($ϵ=0$), the eigenstates are symmetric/antisymmetric superpositions split by $2t_c$. Coherent charge oscillations between dots demonstrated by pulsed gate voltage.

Key limitation: Charge is directly coupled to electric field fluctuations in the solid-state environment → very short coherence times ($T_2^{\ast }\sim 1$ ns). This motivated the pivot to spin-based encodings.

Key Metrics

Metric	Value	Notes	Fidelity reference
Qubit coherence $T_1$	~10 ns	Charge relaxation	Hayashi et al. 2003
Qubit coherence $T_2$	~1 ns	Dominated by charge noise	Hayashi et al. 2003
Gate time (1Q)	<1 ns	Very fast (voltage pulses)	—
Gate fidelity (1Q)	~90%	Limited by decoherence	Petersson et al. 2010
Readout fidelity	~95%	Quantum point contact	Petersson et al. 2010
Qubit footprint	~100–200 nm	Double quantum dot	—
Operating temperature	20–100 mK	GaAs heterostructure	—

Related Qubits

• loss-divincenzo-qubit — spin encoding (much longer $T_2$)
• singlet-triplet-qubit — spin encoding in same platform
• cooper-pair-box-charge-qubit — superconducting charge qubit analogue