Quantum Point Contact¶

A short, narrow electronic constriction whose transverse dimensions are comparable to carrier wavelength, so transport proceeds through a small tunable set of quantum modes and ballistic conductance develops approximately quantized plateaus under suitable low-scattering conditions.

Version: v1 · 2026-09-28 · History
Domain-specific #: 7738
Domain group: Natural Sciences
Origin domain: Physics
Subdomain: Mesoscopic Physics → Physics
Aliases: QPC, Ballistic Point Contact

Core Idea¶

A Quantum Point Contact (QPC) is a short constriction between wider conducting regions whose transverse width is comparable to the electronic wavelength.^[1] Confinement permits only a discrete set of transverse modes to propagate. As a gate or geometry widens the constriction, modes open one by one, and the low-temperature conductance can form plateaus near integer multiples of the conductance quantum under ballistic, adiabatic, and low-reflection conditions.^[2]

The canonical semiconductor realization begins with a high-mobility two-dimensional electron gas. Two negatively biased split gates deplete carriers below them and leave a narrow saddle-shaped channel between source and drain reservoirs. Gate voltage tunes the constriction width and potential. Break junctions, scanning probes, nanowires, graphene structures, and atomic contacts can realize related point-contact behavior through different material mechanisms.

“Point” is not a literal zero-dimensional mathematical point. The constriction has finite length and width. The name indicates that its active cross-section is small enough for wave confinement and that it joins reservoirs through a localized bottleneck. Treating it as a classical point resistor misses the defining modal structure.

In a simple Landauer description,

G = (2e²/h) Σn Tn,

where Tn is the transmission probability of mode n and the factor two reflects spin degeneracy under the usual zero-field assumptions. If N modes transmit almost perfectly, G approaches N(2e²/h). Plateaus emerge because changing the width over a range does not change the number of open subbands, while a step occurs when another subband crosses the reservoir chemical potential.

The familiar unit 2e²/h is conditional. Magnetic field, spin splitting, valley degeneracy, superconductivity, material band structure, interactions, and measurement convention can change degeneracies or plateau sequence.^[3] The more general invariant is conductance organized by discrete propagating channels and their transmissions, not a promise that every QPC trace contains exact integer multiples of one displayed number.

Ballistic transport means carriers cross the active constriction with little momentum-randomizing scattering relative to the relevant length. Adiabatic coupling means the confining potential changes gently enough to suppress intermode reflection. Finite temperature broadens occupation, disorder reduces transmission, and series resistance shifts measured values. The quantization is therefore a regime-dependent observation, not simply a property of any narrow wire.

The reservoirs are essential to two-terminal conductance.^[4] Even a perfectly transmitting short channel exhibits a finite conductance quantum because injection and mode occupancy are set by contacts and reservoirs. Calling the result an ordinary dissipative resistance located wholly inside the constriction can be misleading; energy relaxation may occur in reservoirs while the contact imposes a finite transport relation.^[5]

The 1988 experiments by van Wees and colleagues and independently by Wharam and colleagues demonstrated conductance steps in split-gate semiconductor structures.^[6] Their result provided direct evidence that transverse momentum and one-dimensional subbands govern mesoscopic current. Historical attribution matters, but the abstraction is the device relation rather than one specimen or laboratory.

A QPC can act as more than a conductance demonstration. Because transmission responds strongly to nearby electrostatic charge, it can serve as a charge detector for quantum dots. It can partition electron flow for shot-noise studies, couple quantum Hall edge channels, define tunable barriers, form part of interferometers, and spectroscopically probe subbands and spin effects. These are applications of the same mode-controlled constriction.

Electron–electron interaction produces important departures from the noninteracting staircase. The 0.7 anomaly is a shoulder or plateau-like feature near 0.7 times 2e²/h observed in many QPCs. Its detailed interpretation has involved spin, Kondo-like, and many-body accounts and should not be stated as one settled mechanism.^[7] The anomaly is evidence that the simple independent-channel model is a baseline, not an exhaustive theory.

The term must be distinguished from a quantum dot. A dot confines carriers in multiple spatial directions and supports discrete localized states with charging or resonant phenomena. A QPC is an open constriction supporting propagating modes, although gates can tune a device from open contact toward tunneling or accidental localized states.^[8] Geometry alone does not settle the operating regime.

It is also distinct from a classical point contact used only to characterize bulk transport or spectroscopy. Quantum point contacts require the confinement and transport conditions that make wave modes load-bearing. Atomic-scale metallic contacts can show conductance quantization, but material-specific channel transmissions may prevent equal plateaus even when the Landauer picture applies.

Operational identification requires more than a micrograph. One should declare dimensions relative to wavelength and mean free path, reservoir geometry, temperature, bias, gate configuration, degeneracy, series-resistance correction, and evidence for subband opening. A narrow constriction in a strongly diffusive regime may be a nanoconstriction without exhibiting QPC behavior in the relevant measurement.

Structural Signature¶

Sig role-phrases:

the electronic reservoirs — wider conducting regions establish carrier occupations and electrochemical potentials on either side of the device.
the localized constriction — a short, narrow conducting region couples the reservoirs through a finite bottleneck.
the wavelength-scale cross-section — transverse dimensions comparable to carrier wavelength make quantum confinement load-bearing.
the confined subbands — allowed transverse states form a discrete spectrum of one-dimensional propagating modes.
the tuning coordinate — gate voltage, mechanical separation, or geometry moves subband thresholds and changes transmissions.
the open-mode inventory — the few channels lying below the occupied reservoir energy carry current through the constriction.
the transmission weights — reflection and mode coupling set each channel's contribution rather than guaranteeing perfect passage.
the Landauer relation — conductance is assembled from the conductance quantum, degeneracies, and channel transmissions.
the staircase signature — mode openings create stepwise or channel-resolved conductance structure under suitable conditions.
the ballistic qualification — low scattering, sufficiently low temperature, controlled bias, and adiabatic coupling preserve the ideal modal picture.
the model boundary — interactions, disorder, series resistance, lifted degeneracy, tunneling, or localization qualify or replace the simple quantized staircase.

What It Is Not¶

Not a literal zero-dimensional point. A QPC is a finite, localized constriction whose transverse width is comparable to the electronic wavelength and whose longitudinal direction connects conducting reservoirs.^[9]
Not any narrow wire or metal neck. Recognition requires discrete confined modes and channel-resolved transmission; a classical bottleneck with no wavelength-scale modal structure does not qualify.
Not an ordinary resistor localized wholly inside the constriction. In the Landauer picture, reservoirs set occupation and injection, and energy relaxation can occur outside an otherwise ballistic channel while two-terminal conductance remains finite.
Not a quantum dot. A dot localizes states in all directions and supports charging or discrete-level transport, whereas a QPC's defining states propagate through an open constriction.
Not a guarantee of exact integer multiples of 2e²/h. Imperfect transmission, temperature, bias, series resistance, lifted spin or valley degeneracy, material structure, and interactions can change or smear the plateau sequence.
Not the quantum Hall effect. QPCs can manipulate quantum Hall edge channels and evolve toward related conductance structures under magnetic field, but their zero-field modal quantization has a distinct constriction-and-reservoir identity.

Scope of Application¶

Quantum Point Contact has a domain-bounded mesoscopic-device identity: it applies where a finite electronic constriction between reservoirs is narrow enough for transverse confinement and supports a small set of propagating quantum modes.^[10] Every habitat must specify carrier and dimensionality, geometry, temperature, bias, scattering regime, degeneracy, contacts, and series-resistance treatment rather than infer the identity from small size alone.

Split-gate two-dimensional electron gases. Electrostatic depletion defines a tunable saddle-like constriction whose subband thresholds and conductance staircase can be followed as gate voltage changes.
Semiconductor nanostructures and heterostructures. High-mobility channels support few-mode ballistic transport when the constriction length, carrier wavelength, mean free path, and reservoir coupling lie in the required regime.
Graphene and other multivalley materials. Point contacts are literal when confined electronic modes connect reservoirs, but spin, valley, edge, and band-structure degeneracies must be included in the expected sequence.
Nanowire constrictions. Gates or geometry can select a few one-dimensional subbands, provided transport remains open and propagating rather than dominated by an accidental localized island.
Break junctions and atomic contacts. Atomic-scale necks can be analyzed through channel transmissions even when material-specific orbital channels prevent an equal plateau staircase.
Charge sensing near quantum dots. A QPC operated on a sensitive transmission slope detects nearby electrostatic changes without becoming identical to the localized dot it monitors.
Shot-noise and electron-partition experiments. Tunable transmission through a few channels permits tests of partition statistics when bias, temperature, and reservoir assumptions are controlled.
Quantum Hall edge-channel control. A constriction can partition or couple field-defined edge modes, with the magnetic-field regime and lifted degeneracies declared separately from zero-field QPC behavior.
Mesoscopic interferometers and tunable barriers. QPCs define beam splitters, injectors, or adjustable couplings when their open-mode transmissions remain the operative variables.
Subband and interaction spectroscopy. Gate, source–drain bias, temperature, and magnetic field are used to infer subband spacings, spin structure, and deviations such as the 0.7 feature without assigning an unsettled many-body mechanism by default.
Transition-to-tunneling studies. The device remains in scope while tuning traces the boundary from open few-mode transport toward pinch-off; once localized-state or tunnel-junction behavior becomes constitutive, the applicable device identity changes.

Clarity¶

Naming a quantum point contact makes a mode-selecting constriction legible where a micrograph or resistance trace alone can mislead. It separates the finite physical device from an ideal saddle-point model and from the measured conductance staircase. A device can remain a QPC when temperature, disorder, reflection, interactions, or series resistance blur its plateaus; conversely, a staircase-like trace does not by itself establish transverse subbands and propagating quantum modes.

The name sharpens the boundary between an open few-mode channel, a localized quantum dot, a tunnel junction, and an ordinary diffusive neck. It also forces the conductance convention into view: e²/h is the contribution of one nondegenerate channel, whereas 2e²/h assumes spin degeneracy. The better transport question is: what evidence ties the observed structure to mode opening in this constriction, and which reservoirs, transmission probabilities, degeneracies, temperature, field, bias, and series-resistance treatment determine the reported plateau sequence?

Manages Complexity¶

A Quantum Point Contact compresses the wave mechanics of a narrow constriction into a finite list of propagating transverse modes. The analyst tracks each subband threshold, transmission probability, degeneracy, reservoir chemical potential, and the gate or geometric coordinate that opens the channel. The Landauer sum then makes transport branches readable: between thresholds the open-mode count is stable and conductance forms a plateau; crossing a threshold adds a channel; reflection lowers a mode's contribution; and a magnetic field can lift spin degeneracy and change the step sequence. A conductance trace becomes a channel inventory rather than an undifferentiated resistance curve.

The compression stops when independent, adiabatically connected channels cease to describe the device. Finite temperature and bias smear occupations, disorder and trapping mix or reflect modes, series resistance alters the measured plateau values, and electron interactions produce structure such as the 0.7 anomaly. Reservoirs and contacts remain part of the two-terminal relation, so the conductance quantum is not simply dissipation localized inside the neck. The modal description organizes departures from an ideal staircase, but it cannot by itself distinguish an open QPC from tunneling or accidental localization, or fix the mechanism of an interaction-sensitive anomaly.

Abstract Reasoning¶

Forward reasoning begins with the constriction potential, reservoir chemical potential, degeneracies, and mode transmissions. Transverse confinement determines a sequence of subband thresholds; every threshold below the occupied reservoir energy contributes a propagating channel. Summing the transmissions predicts conductance through the Landauer relation. As a split-gate voltage changes continuously, the open-channel count remains fixed between threshold crossings and then changes discretely, producing a staircase only when temperature, bias, reflection, and series resistance are sufficiently controlled.

Diagnostic reasoning inverts that model cautiously. Repeated conductance structure that shifts systematically with gate voltage can support subband opening when plateau spacing agrees with the declared spin or valley degeneracy and corrections. A magnetic field that lifts spin degeneracy predicts a changed step sequence; raising temperature predicts broadened thresholds; additional reflection predicts reduced contributions from affected modes. These interventions distinguish modal transport from an arbitrary resistance fluctuation, but the trace alone cannot prove that the constriction is ballistic or exclude accidental localized states.

Regime classification asks which description remains valid. If the channel is open and propagating, transmissions and reservoirs organize the result; if gate tuning creates a tunnel barrier or localized island, quantum-dot or tunneling models become appropriate. The 0.7 feature is a diagnostic departure from the independent-channel baseline, not a license to assign one unsettled microscopic cause. Likewise, a finite two-terminal resistance under nearly perfect transmission does not locate ordinary dissipation entirely in the constriction, because injection and equilibration involve the reservoirs. The warranted inference therefore moves from a specified device and measurement regime to a mode inventory and bounded transmission model, with anomalies retained as evidence against overextending that baseline.

Knowledge Transfer¶

Within mesoscopic electron transport, the QPC framework transfers literally across split-gate two-dimensional electron gases, graphene and nanowire constrictions, break junctions, atomic contacts, charge sensing, shot-noise experiments, and quantum-Hall edge partitioning when an open constriction supports a small set of propagating modes between reservoirs. The carried mechanism is transverse confinement followed by mode-dependent Landauer transmission; the diagnostics track subband thresholds, plateau spacing, degeneracy, reflection, temperature, bias, and series resistance. Gate voltage, magnetic field, geometry, or nearby charge provide interventions that change the predicted mode count or transmissions while distinguishing an open QPC from tunneling, a localized quantum dot, or a diffusive neck.

Beyond electronic mesoscopics, the honest transfer is (B) shared abstract mechanism through Channel, with an (A) analogy boundary around the device name. Optical and acoustic waveguides and cold-atom constrictions can literally share the relation between transverse confinement, discrete modes, and stepwise capacity. What travels is the modal-channel reasoning; what remains home-bound is electron charge, Fermi reservoirs, e²/h, spin or valley degeneracy, gate-defined subbands, contact resistance, and the electronic Landauer conductance measured for a QPC. Those other systems are not quantum point contacts simply because their modes are quantized. The stopping boundary is loss of a wavelength-scale electronic constriction between reservoirs, after which the shared lesson belongs to Channel and mode decomposition rather than this device abstraction.

Examples¶

Canonical¶

In a high-mobility GaAs/AlGaAs two-dimensional electron gas, a pair of split gates depletes carriers beneath the metal and leaves a narrow channel between two wider reservoirs. Making the gate voltage more negative raises the constriction's transverse subband thresholds. When two spin-degenerate modes transmit nearly perfectly, the Landauer sum gives conductance near \(2(2e^2/h)\); after one threshold rises above the occupied reservoir energy, the conductance falls to about \(2e^2/h\). Plateaus persist between threshold crossings because the open-mode count is unchanged. Temperature, reflection, lifted degeneracy, and series resistance can smear or shift those values without erasing the device identity.

Mapped back: The two-dimensional regions are the electronic reservoirs, and the depleted opening is the localized constriction with the wavelength-scale cross-section. Gate voltage is the tuning coordinate; subband thresholds form the confined subbands and determine the open-mode inventory. Near-unit the transmission weights enter the Landauer relation, producing the staircase signature only under the ballistic qualification.

Applied / In Practice¶

A QPC placed electrostatically beside a quantum dot can be biased on a steep part of one conductance step. When the dot gains or loses an electron, its nearby electrostatic potential shifts the constriction and changes the QPC transmission, so a small conductance change reports the dot's charge transition. The sensing channel remains open and propagating; the dot is the localized system being measured, not another name for the QPC. If an unintended localized state forms inside the constriction, the simple charge-sensitive transmission account must be reconsidered.

Mapped back: The nearby charge perturbs the tuning coordinate, which changes the transmission weights of the open-mode inventory and hence the conductance assembled by the Landauer relation. Keeping the detector channel distinct from the localized dot enforces the model boundary. The case uses the QPC's mode-sensitive conductance rather than inferring its identity from a narrow geometry alone.

Structural Tensions¶

T1: Continuous tuning versus discrete mode count. Gate voltage or geometry varies smoothly, yet conductance can remain nearly constant until a confined subband crosses the reservoir chemical potential. Treating the staircase as purely continuous misses the threshold structure, while treating each step as exact ignores transmission and measurement conditions.

Diagnostic: Do observed plateaus and transitions track subband thresholds under the declared tuning coordinate rather than merely resemble a staircase?

T2: Ideal quantization versus imperfect transmission. Near-unit channel transmissions make integer plateaus legible, but disorder, reflection, and intermode coupling can reduce or reshape them without automatically destroying QPC identity. Insisting on perfect steps excludes real devices; accepting any irregular trace makes the modal claim unfalsifiable.

Diagnostic: Are departures from ideal plateaus accounted for through independently supported channel transmissions and scattering conditions?

T3: Local constriction versus reservoir-defined transport. The bottleneck selects propagating modes, while reservoir occupations, contacts, and series resistance help determine two-terminal conductance. Localizing the entire measured resistance inside the constriction erases that system relation, whereas ignoring the constriction erases the mode filter.

Diagnostic: Does the transport account separate constriction transmission from reservoir injection, equilibration, and external series resistance?

T4: Universal conductance scale versus system-specific degeneracy. The Landauer contribution per nondegenerate channel is structurally stable, yet spin, valley, magnetic-field, material, and convention choices alter the displayed plateau sequence. Quoting 2e²/h without its degeneracy assumptions turns a conditional regularity into a universal promise.

Diagnostic: Are channel degeneracies and the conductance-quantum convention declared before plateau spacings are compared?

T5: Independent-channel baseline versus many-body structure. A noninteracting mode sum gives a powerful baseline, while features such as the 0.7 anomaly show that interactions can be load-bearing. Assigning every departure to disorder hides collective physics; assigning one settled microscopic explanation overstates what the evidence establishes.

Diagnostic: Is an anomalous feature identified relative to the independent-channel prediction while competing interaction and imperfection accounts remain distinguishable?

T6: Open propagation versus localization. Tightening the constriction can move a device from a few open modes toward tunneling or an accidental localized state. Geometry changes continuously across that boundary, but the relevant transport identity changes when localized levels rather than propagating channels govern the response.

Diagnostic: What evidence shows that the active states remain propagating modes between reservoirs rather than a tunnel barrier or quantum-dot-like localized island?

T7: Compact geometric label versus regime-dependent identity. “Point contact” efficiently names a localized bottleneck, although the device has finite length and width and need not display ideal quantization in every measurement. Size alone is insufficient, but demanding one canonical fabrication would exclude legitimate wavelength-scale realizations.

Diagnostic: Are finite geometry, carrier wavelength, scattering length, bias, and temperature jointly consistent with a mode-selecting mesoscopic constriction?

T8: Quantum Point Contact autonomy versus reduction to Channel (Channel). The parent Prime carries the portable structure of a bounded conduit. Every quantum point contact is a strict kind of Channel because it provides a constrained passage between electronic reservoirs, but the child additionally requires wavelength-scale transverse confinement, propagating subbands, transmissions, and Landauer conductance. Reduction loses the quantum transport regime; total autonomy hides the general conduit structure.

Diagnostic: Does the account retain the electronic-mode and reservoir conditions as necessary differentia of this Channel?

Structural–Framed Character¶

Quantum Point Contact is structural-leaning. Its vocab_travels is moderate because reservoirs, confined subbands, Landauer transmission, ballistic transport, and conductance plateaus are mesoscopic-physics terms, while a bounded conduit with constrained modes is widely intelligible. Its evaluative_weight is low: conductance and transmission are physical relations, although device usefulness depends on experimental aims. Its institutional_origin concerns the apparatus and model used to realize and measure the contact, not the underlying transport dependence. Its human_practice_bound is low because confined propagating modes and scattering exist without an observer. On import_vs_recognize, gate geometry and measurement conventions are imposed, but the channel inventory and its conductance consequences are recognized physical structure.

The smallest reviewed portable skeleton is Channel: source and receiver reservoirs are joined by a bounded medium with an admissible mode inventory, finite capacity, and transmission losses. Portable and cross-domain reach belongs to that Prime. A Quantum Point Contact adds wavelength-scale confinement, electronic subbands, degeneracy, the Landauer relation, ballistic and adiabatic qualifications, and the conductance staircase. These mesoscopic conditions distinguish it from a generic channel and from a narrow classical resistor or localized quantum dot.

Its character: structural-leaning because a physical conduit-and-mode organization closely realizes the portable Channel skeleton, while quantum confinement and mesoscopic transport laws provide the indispensable domain frame.

Structural Core vs. Domain Accent¶

This decomposition explains why Quantum Point Contact is a domain-specific abstraction rather than a Prime.

What is skeletal (could lift toward a cross-domain prime). Source and receiver endpoints are joined by a bounded medium whose admissible modes, finite capacity, and transmission losses constrain what can cross. The invariant is a directed conduit whose internal constraints select and shape transmission, and recognition fails if there is no endpoint coupling or no bounded propagating-mode inventory. Quantum Point Contact is therefore a strict specialization of Channel: Channel supplies the source–medium–receiver organization and constitutive capacity boundary, while the child realizes it as a wavelength-scale electronic constriction.

What is domain-bound. Wider electronic reservoirs provide occupations, a finite constriction produces transverse quantum subbands, and gate voltage or geometry tunes which few propagating modes lie open. Mode transmissions and degeneracies enter the Landauer conductance relation, while low temperature, controlled bias, ballisticity, adiabatic coupling, series resistance, disorder, interactions, and localization delimit the staircase model. A classical neck, tunnel junction, or localized quantum dot lacks the required open reservoir-to-reservoir modal channel even if its geometry looks narrow.

Why this does not clear the prime bar. The complete electronic-reservoir, wavelength-scale-constriction, confined-subband, tuning-coordinate, transmission-weight, Landauer, conductance-staircase, and regime-boundary signature does not recur literally across at least three unrelated domains with the same recognition and failure conditions. Knowledge Transfer gives confined-mode carriage to Channel; optical, acoustic, or cold-atom constrictions may share that mechanism, but they are not Quantum Point Contacts without electronic transport and its conductance relation. Removing the mesoscopic-electronic accent leaves a bounded modal Channel but not a Quantum Point Contact, while removing the source–receiver conduit and its constrained mode inventory leaves a nanostructure or measurement trace without the Channel structure that makes the device an open contact.

This entry is a kind of Channel.

Instantiates — Channel (Channel). The two electronic reservoirs are source and receiver, and the localized wavelength-scale constriction is the bounded medium between them. Transverse confinement supplies an admissible mode alphabet and finite mode count; channel transmissions encode reflection and distortion; and the Landauer relation turns that constrained inventory into conductance. A mode above the occupied energy or one suppressed by the constriction is structurally unavailable to transport, matching Channel's constitutive capacity and codebook boundary. Remove the reservoir-to-reservoir conduit or its confined propagating modes and the QPC ceases to be an open quantum point contact, while the parent Channel signature collapses with it. Electronic subbands, degeneracies, ballistic qualification, and the conductance staircase are the mesoscopic residual.

Relationships to Other Abstractions¶

Current abstraction Quantum Point Contact Domain-specific

Parents (1) — more general patterns this builds on

Quantum Point Contact is a kind of Channel Prime

The two electronic reservoirs are source and receiver, and the localized wavelength-scale constriction is the bounded medium between them.

Hierarchy path (1) — routes to 1 parentless root

Quantum Point Contact → Channel

Neighborhood in Abstraction Space¶

Quantum Point Contact sits in a moderately populated region (57^th percentile for distinctiveness): it has near-neighbors but no dense thicket of look-alikes.

Family — Quantum Electronic States & Transport (12 abstractions)

Nearest neighbors

Computed from structural-signature embeddings · 2026-10-08

Not to Be Confused With¶

Quantum Dot. A quantum dot confines carriers in all relevant directions and supports localized discrete states, whereas a quantum point contact is an open constriction with propagating transverse modes. Tell: isolated resonant levels and charge occupancy identify a dot; conductance steps as open modes enter identify a point contact.
Classical Point Contact. A classical point contact is a small constriction whose conductance is governed without load-bearing quantum mode quantization. Tell: reproducible plateaus tied to integer transmitted modes support the quantum identity, while smooth geometry-dependent conductance without those modes remains classical.
Tunnel Junction. A tunnel junction transports carriers primarily through a classically forbidden barrier, while an open quantum point contact transmits available modes through a saddle-like constriction. Tell: exponential barrier sensitivity and resonant tunneling identify a junction; opening and closing propagating channels identify a QPC.
Conductance Quantum. The conductance quantum is the unit that scales an ideally transmitted mode's contribution; it is a parameter in the QPC relation rather than the device. Tell: a numerical conductance scale is the quantum, while a gate-defined constriction with tunable transmission eigenvalues is the QPC.
Ballistic Transport. Ballistic transport is a regime with negligible scattering over the relevant path and can occur in many device geometries; it is a supporting condition, not the contact itself. Tell: long mean free path establishes the regime, whereas transverse confinement and a tunable bottleneck establish the QPC.
Quantum Hall Point Contact. A quantum Hall point contact is a QPC operated in magnetic field to partition edge channels, a specialized regime of the broader device. Tell: transport organized by quantum-Hall edge channels identifies the subtype; zero-field transverse subbands suffice for an ordinary QPC.
Nanowire. A nanowire is an extended narrow conductor that may contain, form, or couple to a point contact but does not require a localized tunable bottleneck. Tell: a constriction shorter than the extended channel and controlling modal transmission is the QPC within the wire.
0.7 Anomaly. The 0.7 anomaly is an interaction-sensitive conductance feature observed in many QPCs, not the definition of the device. Tell: a shoulder near a fraction of the first plateau is the anomaly; quantized-mode transport through the constriction identifies the QPC whether or not the shoulder appears.

References¶

[1] Quantized Conductance of Point Contacts in a Two-Dimensional Electron Gas registry ↩

[2] Unverified encyclopedia synthesis; claim-specific authoritative support was not established in this verification pass. ↩

[3] Unverified encyclopedia synthesis; claim-specific authoritative support was not established in this verification pass. ↩

[4] Unverified encyclopedia synthesis; claim-specific authoritative support was not established in this verification pass. ↩

[5] Unverified encyclopedia synthesis; claim-specific authoritative support was not established in this verification pass. ↩

[6] Unverified encyclopedia synthesis; claim-specific authoritative support was not established in this verification pass. ↩

[7] Unverified encyclopedia synthesis; claim-specific authoritative support was not established in this verification pass. ↩

[8] Unverified encyclopedia synthesis; claim-specific authoritative support was not established in this verification pass. ↩

[9] Unverified encyclopedia synthesis; claim-specific authoritative support was not established in this verification pass. ↩

[10] Unverified encyclopedia synthesis; claim-specific authoritative support was not established in this verification pass. ↩