---
title: "Quantum & fields — Sandbox Physics"
description: "Build a picture of the invisible, one measurement at a time."
canonical_url: "https://sandboxphysics.com/topics/quantum/"
language: "en"
page_type: "lab-directory"
alternate_languages:
  zh-CN: "https://sandboxphysics.com/zh/topics/quantum/"
last_modified: "2026-10-24"
---

[← All Labs](https://sandboxphysics.com/labs/) 04 / 04

Particles · Probability · Measurement

# Quantum & fields

Build a picture of the invisible, one measurement at a time.

129 experiments

Start here

## Start from a single measurement

Predict an outcome, then count what the measurements actually give. The path starts with one qubit and moves on to wave packets, bound states and two-photon interference.

6 Labs · about 120 min

1. [01 Observe Quantum State & Born Measurement Predict a probability, turn the analyzer, then compare your prediction with the measured frequency over many shots. 15 min](https://sandboxphysics.com/labs/qubit-state/)
2. [02 Compare Stern–Gerlach Sequence Turn the middle magnet to a crossed axis and compare it with the same-axis case. What does the middle measurement change? 15 min](https://sandboxphysics.com/labs/stern-gerlach-sequence/)
3. [03 Model Wave Packet & Uncertainty Release a narrow packet and a wide one. Which spreads faster, and how can a focused packet first get narrower? 20 min](https://sandboxphysics.com/labs/wave-packet-uncertainty/)
4. [04 Model Quantum Harmonic Oscillator Start from the ground state, then mix in a second level or displace the state. When does the probability cloud move, and what do sampled positions show? 20 min](https://sandboxphysics.com/labs/quantum-harmonic-oscillator/)
5. [05 Compare Which Path & Quantum Eraser Tag the two paths, then erase the which-path information. Do the fringes come back in all the data, or only after the detections are sorted into groups? 25 min](https://sandboxphysics.com/labs/quantum-eraser/)
6. [06 Transfer Hong–Ou–Mandel Two-Photon Interference Scan the arrival delay of two photons and watch coincidences drop when they become indistinguishable. 25 min](https://sandboxphysics.com/labs/hong-ou-mandel/)

## Browse the collection

Find an experiment

129 experiments

1. [Quantum & fields Decay Chain Counter Why can daughter counts rise while the parent source is decaying? 15 min](https://sandboxphysics.com/labs/decay-chain-counting/)
2. [Quantum & fields Proton Form Factors How can scattered electrons separate a proton’s electric and magnetic responses? 15 min](https://sandboxphysics.com/labs/nuclear-form-factor/)
3. [Quantum & fields Nuclear Shell Filling How does spin–orbit splitting open a shell gap at twenty-eight neutrons? 15 min](https://sandboxphysics.com/labs/nuclear-shell-filling/)
4. [Quantum & fields SQUID: Flux into Voltage How can a magnetic flux change a superconducting circuit’s voltage? 15 min](https://sandboxphysics.com/labs/squid-flux-response/)
5. [Quantum & fields Josephson Switching Statistics Why does a biased Josephson junction switch before its critical current? 15 min](https://sandboxphysics.com/labs/josephson-switching-statistics/)
6. [Quantum & fields Superconductors in a Magnetic Field Why can a magnetic field enter one superconductor before it becomes normal? 15 min](https://sandboxphysics.com/labs/superconductor-critical-fields/)
7. [Quantum & fields How Cooper Pairs Condense How do loose Cooper pairs turn smoothly into tightly bound molecules that condense? 16 min](https://sandboxphysics.com/labs/bec-bcs-crossover/)
8. [Quantum & fields Weak Decay and the Mirror Test Why does reversing the nuclear spin reverse the preferred electron direction? 15 min](https://sandboxphysics.com/labs/weak-decay-parity/)
9. [Quantum & fields Neutral Kaons in Flight How can a neutral kaon change flavour while its probability of survival falls? 20 min](https://sandboxphysics.com/labs/neutral-kaon-interferometer/)
10. [Quantum & fields Inside the Proton What do a scattered electron’s energy and direction reveal about the proton? 20 min](https://sandboxphysics.com/labs/deep-inelastic-scattering/)
11. [Quantum & fields Quantum Phase Estimation In quantum phase estimation, how much more evolution does each extra bit of precision need? 25 min](https://sandboxphysics.com/labs/quantum-phase-estimation/)
12. [Quantum & fields Grover Amplitude Amplification Can one extra round make the answer harder to find? 25 min](https://sandboxphysics.com/labs/grover-amplitude-amplification/)
13. [Quantum & fields Resonant Tunneling Transport Can two barriers transmit better than one? 20 min](https://sandboxphysics.com/labs/resonant-tunneling-transport/)
14. [Quantum & fields Gravitational Quantum Bouncer How tall must a slit be for a neutron to get through? 20 min](https://sandboxphysics.com/labs/gravitational-quantum-bouncer/)
15. [Quantum & fields Thouless Transport Pump How can slowly cycling a chain's parameters back to their start still move particles across it? 20 min](https://sandboxphysics.com/labs/thouless-quantum-pump/)
16. [Quantum & fields Spin Squeezing Metrology Does squeezing the noise of a spin ensemble always give a more precise measurement? 20 min](https://sandboxphysics.com/labs/spin-squeezing-metrology/)
17. [Quantum & fields Quantum Spin Chain Quench If you flip one spin in a chain, where does its influence go? 20 min](https://sandboxphysics.com/labs/quantum-spin-chain-quench/)
18. [Quantum & fields Quantum State & Process Tomography Can measuring along one direction reveal a whole quantum state? 20 min](https://sandboxphysics.com/labs/quantum-state-process-tomography/)
19. [Quantum & fields Quantum Error Correction Can you find an error without reading the encoded message? 20 min](https://sandboxphysics.com/labs/quantum-error-correction/)
20. [Quantum & fields Identical Atom Exchange When two atoms in neighboring traps tunnel at the same time, do they end up together or apart? 18 min](https://sandboxphysics.com/labs/identical-atom-exchange/)
21. [Quantum & fields Quantum Gas Occupation When the same trap is cooled, which particles crowd into the lowest energy level? 18 min](https://sandboxphysics.com/labs/quantum-gas-occupation/)
22. [Quantum & fields Hydrogen Orbitals & Spectra Why can a hydrogen spectral line be missing even when the energy gap matches? 20 min](https://sandboxphysics.com/labs/hydrogen-orbitals-spectra/)
23. [Quantum & fields Partial-Wave Scattering Why does scattering off a single round target show so many minima? 20 min](https://sandboxphysics.com/labs/partial-wave-scattering/)
24. [Quantum & fields Franck–Hertz Excitation Why can a higher voltage make the current drop? 20 min](https://sandboxphysics.com/labs/franck-hertz-excitation/)
25. [Quantum & fields Laser Cooling & MOT Can light slow an atom down and also hold it in place? 20 min](https://sandboxphysics.com/labs/laser-cooling-magneto-optical-trap/)
26. [Quantum & fields Homodyne Quantum Tomography Can you draw a quantum state from detector noise? 20 min](https://sandboxphysics.com/labs/homodyne-quantum-tomography/)
27. [Quantum & fields Quantum Phase Metrology Do sharper interference fringes always mean a better phase measurement? 20 min](https://sandboxphysics.com/labs/quantum-phase-metrology/)
28. [Quantum & fields Coupled Spin Spectroscopy Why can a spectral line be missing even though both levels exist? 18 min](https://sandboxphysics.com/labs/coupled-spin-spectroscopy/)
29. [Quantum & fields Transmon Artificial Atom What do you give up when you make an artificial atom less sensitive to stray charge? 18 min](https://sandboxphysics.com/labs/transmon-artificial-atom/)
30. [Quantum & fields Quantum Zeno Monitoring Can repeated checks slow a quantum transition? 18 min](https://sandboxphysics.com/labs/quantum-zeno-monitoring/)
31. [Quantum & fields Two-Level Quantum Otto Engine Can one spin turn heat into work? 18 min](https://sandboxphysics.com/labs/quantum-otto-engine/)
32. [Quantum & fields Aharonov–Bohm Flux Interferometer Can a magnetic field the electrons never pass through change which exit they take? 18 min](https://sandboxphysics.com/labs/aharonov-bohm-flux/)
33. [Quantum & fields Atom Interferometer Gravimeter How can three laser pulses measure gravity with falling atoms? 18 min](https://sandboxphysics.com/labs/atom-interferometer-gravimeter/)
34. [Quantum & fields Anderson Localization Can a wave get stuck without a wall? 20 min](https://sandboxphysics.com/labs/anderson-localization-transport/)
35. [Quantum & fields Bloch Oscillations Why does a steady push make a particle in a lattice swing back and forth instead of speeding up? 20 min](https://sandboxphysics.com/labs/bloch-oscillation-dynamics/)
36. [Quantum & fields Trapped-Ion Sideband Spectroscopy Why does the red sideband disappear when a trapped ion reaches its motional ground state? 25 min](https://sandboxphysics.com/labs/trapped-ion-sideband-spectroscopy/)
37. [Quantum & fields Cavity Quantum Excitation Exchange Can a cavity give a photon back to the atom that emitted it? 25 min](https://sandboxphysics.com/labs/cavity-quantum-exchange/)
38. [Quantum & fields STIRAP Dark-State Transfer How can two laser pulses transfer an atom while it almost never sits in the lossy middle state? 25 min](https://sandboxphysics.com/labs/stirap-dark-state-transfer/)
39. [Quantum & fields Rydberg Atom Blockade Why are two nearby atoms rarely excited to Rydberg states at the same time? 25 min](https://sandboxphysics.com/labs/rydberg-atom-blockade/)
40. [Quantum & fields Fluorescence & Quantum Jumps When the detector goes quiet, has the atom really gone dark? 25 min](https://sandboxphysics.com/labs/fluorescence-quantum-jumps/)
41. [Quantum & fields HBT Photon Correlation How can you tell equally bright light sources apart by the way their photons arrive? 25 min](https://sandboxphysics.com/labs/hbt-photon-correlation/)
42. [Quantum & fields Quantum Well Spectroscopy How much do the energy levels rise when a quantum well is made narrower? 25 min](https://sandboxphysics.com/labs/quantum-well-spectroscopy/)
43. [Quantum & fields Coherent Double Well Transfer How can a particle get into the other well without climbing over the barrier? 25 min](https://sandboxphysics.com/labs/coherent-double-well-transfer/)
44. [Quantum & fields Wave Packet & Uncertainty Does a narrower wave packet end up spreading wider? 20 min](https://sandboxphysics.com/labs/wave-packet-uncertainty/)
45. [Quantum & fields Quantum Harmonic Oscillator If the probability density of a quantum oscillator never changes, is its energy zero? 20 min](https://sandboxphysics.com/labs/quantum-harmonic-oscillator/)
46. [Quantum & fields Landau–Zener Passage Does a slow sweep through an avoided crossing switch a two-level system into its other state? 25 min](https://sandboxphysics.com/labs/landau-zener-passage/)
47. [Quantum & fields Berry Phase Interferometer How far does an interference fringe shift when a spin is carried around a loop? 25 min](https://sandboxphysics.com/labs/berry-phase-interferometer/)
48. [Quantum & fields Quantum Teleportation & Swapping If the classical message is blocked, does a teleported quantum state still arrive? 25 min](https://sandboxphysics.com/labs/quantum-teleportation/)
49. [Quantum & fields BB84 Key Distribution In BB84, which bits are kept for the key after the two sides compare notes in public? 25 min](https://sandboxphysics.com/labs/bb84-key-distribution/)
50. [Quantum & fields Which Path & Quantum Eraser Can sorting the hits by their which-path tags bring the interference fringes back? 25 min](https://sandboxphysics.com/labs/quantum-eraser/)
51. [Quantum & fields Weak Measurement & Conditional Pointer To make the pointer shift bigger in a weak measurement, how many events must you give up? 25 min](https://sandboxphysics.com/labs/weak-measurement-pointer/)
52. [Quantum & fields Hong–Ou–Mandel Two-Photon Interference When two photons enter a beam splitter from opposite sides, why do the two counters stop clicking together? 25 min](https://sandboxphysics.com/labs/hong-ou-mandel/)
53. [Quantum & fields Bell Correlations & CHSH Can two stations whose results each look random still beat the limit of any local theory? 25 min](https://sandboxphysics.com/labs/bell-chsh/)
54. [Quantum & fields Spin Echo & Noise Spectroscopy Which lost coherence can a pulse bring back? 25 min](https://sandboxphysics.com/labs/spin-echo-noise/)
55. [Quantum & fields Decoherence Channels & Information Loss Does losing phase also mean losing energy? 25 min](https://sandboxphysics.com/labs/decoherence-channels/)
56. [Quantum & fields Quantum State & Born Measurement Can two states look identical in one basis and different in another? 15 min](https://sandboxphysics.com/labs/qubit-state/)
57. [Quantum & fields Stern–Gerlach Sequence Why does a middle analyzer change a repeated measurement? 15 min](https://sandboxphysics.com/labs/stern-gerlach-sequence/)
58. [Quantum & fields Rabi Pulse Calibration How long must a pulse last to flip a state? 15 min](https://sandboxphysics.com/labs/rabi-pulse-calibration/)
59. [Quantum & fields Ramsey Frequency Measurement Can a longer wait reveal a smaller frequency difference? 15 min](https://sandboxphysics.com/labs/ramsey-frequency/)
60. [Quantum & fields Can a Particle Cross an Impossible Wall? Why can a particle sometimes be detected beyond a barrier it classically cannot cross? 10 min](https://sandboxphysics.com/labs/quantum-tunneling/)
61. [Quantum & fields Can One Particle Interfere? How do unpredictable hits accumulate into stable fringes? 12 min](https://sandboxphysics.com/labs/single-particle-interference/)
62. [Quantum & fields How a Field Becomes Quantized How can a continuous field produce discrete particle excitations? 15 min](https://sandboxphysics.com/labs/field-modes/)
63. [Quantum & fields SSH Chain & Edge States Is a particle trapped at the edge of an SSH chain always in a topological state? 20 min](https://sandboxphysics.com/labs/ssh-topological-chain/)
64. [Quantum & fields Chern Insulator · Follow the Edge When the edge of a Chern insulator lights up, does the wave really travel along it? 25 min](https://sandboxphysics.com/labs/chern-insulator/)
65. [Quantum & fields Haldane Lattice · Turn the Phase If you reverse the hopping phase in a Haldane lattice, does the edge carry waves the other way? 25 min](https://sandboxphysics.com/labs/haldane-honeycomb/)
66. [Quantum & fields Cavity Photon Counting & Feedback When can atoms passing through a cavity reveal its photon number, and when can delayed feedback keep that number steady? 25 min](https://sandboxphysics.com/labs/cavity-photon-qnd-feedback/)
67. [Quantum & fields Zeeman Atomic-beam Slower Which atoms does a Zeeman slower actually slow down, and what can the glow of atoms at its exit prove? 22 min](https://sandboxphysics.com/labs/zeeman-atomic-beam-slower/)
68. [Quantum & fields Two-Ion Quantum Logic Spectroscopy How can you take the spectrum of one ion by watching the light from another ion beside it? 25 min](https://sandboxphysics.com/labs/two-ion-quantum-logic-spectroscopy/)
69. [Quantum & fields Three-Photon GHZ Correlation Bench How can three photons whose individual results are random still beat every local explanation? 25 min](https://sandboxphysics.com/labs/three-photon-ghz-correlations/)
70. [Quantum & fields Single-Electron Penning Trap & Spin Readout How can the spin of a single trapped electron be read from the frequency of its motion? 25 min](https://sandboxphysics.com/labs/penning-electron-spin-readout/)
71. [Quantum & fields Molecular-Beam Proton Magnetic Moment How can a beam of hydrogen molecules measure the proton's magnetic moment when the molecules' rotation is magnetic too? 25 min](https://sandboxphysics.com/labs/molecular-beam-proton-moment/)
72. [Quantum & fields Hydrogen–Deuterium Isotope Spectrometer Why do hydrogen and deuterium emit their spectral lines at slightly different wavelengths? 20 min](https://sandboxphysics.com/labs/hydrogen-deuterium-isotope-spectrometer/)
73. [Quantum & fields Two-Isotope Doppler Thermometer How can two hydrogen isotopes give a gas temperature when the spectrometer also blurs the lines? 20 min](https://sandboxphysics.com/labs/two-isotope-doppler-thermometer/)
74. [Quantum & fields Compton Angular Spectrometer How does a scattered photon's energy change with angle, and what does that reveal? 20 min](https://sandboxphysics.com/labs/compton-angular-spectrometer/)
75. [Quantum & fields Compton Coincidence Energy Analyzer Do the scattered photon and the recoiling electron together carry all of the incoming photon's energy? 20 min](https://sandboxphysics.com/labs/compton-coincidence-energy/)
76. [Quantum & fields Continuous-wave NMR Spectrometer How do you find the center and width of a nuclear resonance with a continuous radio-frequency scan? 20 min](https://sandboxphysics.com/labs/cw-nmr-spectrometer/)
77. [Quantum & fields NMR Power Saturation Analyzer Why does the absorption signal of a nuclear resonance shrink when the radio-frequency drive gets too strong? 20 min](https://sandboxphysics.com/labs/nmr-power-saturation/)
78. [Quantum & fields NMR Free Induction Spectrometer What can the fading voltage after a radio-frequency pulse tell you about the nuclear spins? 20 min](https://sandboxphysics.com/labs/nmr-free-induction-spectrometer/)
79. [Quantum & fields NMR Inversion Recovery Relaxometer How do you measure how fast nuclear magnetization recovers after it is flipped? 20 min](https://sandboxphysics.com/labs/nmr-inversion-recovery/)
80. [Quantum & fields Optical Pumping and Relaxation How can light measure how fast atoms relax in the dark? 20 min](https://sandboxphysics.com/labs/optical-pumping-relaxation/)
81. [Quantum & fields Hanle Lifetime Spectrometer How can a magnetic field measure how long an excited atom lives? 20 min](https://sandboxphysics.com/labs/hanle-lifetime-spectrometer/)
82. [Quantum & fields Oil-Drop Charge Measurement How can the way an oil drop moves reveal its electric charge? 20 min](https://sandboxphysics.com/labs/oil-drop-charge/)
83. [Quantum & fields Atomic Magnetic-Moment Comparator How can you measure the electron's spin factor without knowing the magnetic field? 20 min](https://sandboxphysics.com/labs/atomic-magnetic-moment-comparator/)
84. [Quantum & fields Zeeman Polarization Spectrometer What does a spectral line look like in a magnetic field, viewed across and along the field? 20 min](https://sandboxphysics.com/labs/zeeman-polarization-spectrometer/)
85. [Quantum & fields Canal-Ray Doppler Spectrometer How does the light from fast-moving hydrogen atoms reveal their speed? 20 min](https://sandboxphysics.com/labs/canal-ray-doppler-spectrometer/)
86. [Quantum & fields Stark Splitting Spectrometer How can a split hydrogen line measure an electric field? 20 min](https://sandboxphysics.com/labs/stark-splitting-spectrometer/)
87. [Quantum & fields Lamb Shift Microwave Bench How can microwaves find the Lamb shift in hydrogen? 20 min](https://sandboxphysics.com/labs/lamb-shift-microwave/)
88. [Quantum & fields Mössbauer Doppler Observatory Why can a source moving a few millimeters per second resolve tiny shifts in nuclear energy levels? 20 min](https://sandboxphysics.com/labs/mossbauer-doppler-resonance/)
89. [Quantum & fields Blackbody Radiation Observatory Can one temperature and one emissivity explain the measured spectrum? 18 min](https://sandboxphysics.com/labs/blackbody-radiation/)
90. [Quantum & fields The Matter-Wave Antilaser How does the relative phase of two matter waves decide whether a lossy site swallows them? 16 min](https://sandboxphysics.com/labs/coherent-matter-wave-absorber/)
91. [Quantum & fields A Cut That Moves Every Mode Why does cutting one link in a ring where hopping favors one direction push every mode to one edge? 16 min](https://sandboxphysics.com/labs/non-hermitian-skin-effect/)
92. [Quantum & fields When a Molecular Bond Breaks Why can a kicked molecular bond break when an ideal spring of the same stiffness always pulls back? 18 min](https://sandboxphysics.com/labs/morse-molecular-bond-breaking/)
93. [Quantum & fields Through a Conical Intersection What happens to a molecular wavepacket when it passes the point where two energy surfaces touch? 18 min](https://sandboxphysics.com/labs/molecular-conical-intersection/)
94. [Quantum & fields A Quantum Newton’s Cradle Why do two colliding atom clouds keep returning to their starting shape in a harmonic trap but not in a distorted one? 18 min](https://sandboxphysics.com/labs/quantum-newtons-cradle/)
95. [Quantum & fields When Matter-Wave Solitons Collide What decides whether two colliding matter-wave solitons make a bright peak or a dark gap where they meet? 18 min](https://sandboxphysics.com/labs/bright-matter-wave-solitons/)
96. [Quantum & fields Build an Atomic Corral Why does a ring of atoms on a metal surface make the surface electrons form rings of standing waves? 18 min](https://sandboxphysics.com/labs/atomic-quantum-corral/)
97. [Quantum & fields A Quantum Mirage at an Empty Focus Can an atom at one focus of an elliptical corral change the electrons at the other, empty focus? 18 min](https://sandboxphysics.com/labs/elliptical-quantum-mirage/)
98. [Quantum & fields A Giant Atom Hears Its Echo What happens when an atom coupled to a waveguide at two distant points meets its own emitted wave again? 18 min](https://sandboxphysics.com/labs/giant-atom-waveguide-echo/)
99. [Quantum & fields A Photon Cloud That Cannot Escape Why does an excited atom tuned into a waveguide's band gap keep part of its excitation instead of emitting it all? 18 min](https://sandboxphysics.com/labs/bandgap-bound-photon-cloud/)
100. [Quantum & fields Dynamical Casimir Photon Pairs How can you tell that a modulated boundary emits photons in pairs, when each mode alone looks like thermal noise? 18 min](https://sandboxphysics.com/labs/dynamical-casimir-photon-pairs/)
101. [Quantum & fields Single-Atom Photon Blockade How can one atom in a cavity keep a second photon out once the first is inside? 18 min](https://sandboxphysics.com/labs/single-atom-photon-blockade/)
102. [Quantum & fields Andreev Reflection What comes back when an electron hits a superconductor with an energy inside its gap? 18 min](https://sandboxphysics.com/labs/andreev-electron-hole-reflection/)
103. [Quantum & fields Majorana End Modes Why does a superconducting wire with a gapped interior show zero-energy states at its ends? 18 min](https://sandboxphysics.com/labs/kitaev-majorana-end-modes/)
104. [Quantum & fields Airy Matter Waves How can the brightest crest of a free matter wave curve when no force acts on it? 16 min](https://sandboxphysics.com/labs/airy-matter-wave-caustics/)
105. [Quantum & fields Matter-Wave Lens How can one short pulse slow or refocus a spreading matter wave? 16 min](https://sandboxphysics.com/labs/delta-kick-matter-wave-lens/)
106. [Quantum & fields Quantum Billiards How does the shape of a quantum billiard change the pattern a reflected wave makes? 18 min](https://sandboxphysics.com/labs/quantum-wave-billiards/)
107. [Quantum & fields Quantum Time Mirror Can a scattered wave be gathered back into exactly its starting state? 18 min](https://sandboxphysics.com/labs/loschmidt-quantum-time-mirror/)
108. [Quantum & fields Perfect Quantum State Transfer How can a chain with fixed couplings deliver an excitation to the far end with certainty? 18 min](https://sandboxphysics.com/labs/perfect-quantum-state-transfer/)
109. [Quantum & fields Rydberg Many-Body Scars Does an interacting chain of atoms always forget the pattern it started in? 18 min](https://sandboxphysics.com/labs/rydberg-many-body-scars/)
110. [Quantum & fields Aharonov–Bohm Quantum Cage How can a magnetic flux trap a particle in a diamond chain without walls? 18 min](https://sandboxphysics.com/labs/aharonov-bohm-quantum-cage/)
111. [Quantum & fields Repulsively Bound Atom Pair How can two atoms that repel each other move together as a pair? 18 min](https://sandboxphysics.com/labs/repulsively-bound-atom-pair/)
112. [Quantum & fields Dicke Superradiant Burst Why can a group of excited atoms release its light in one bright burst? 18 min](https://sandboxphysics.com/labs/dicke-superradiant-burst/)
113. [Quantum & fields Subradiant Atomic Array How can neighboring atoms keep an excitation from radiating away so quickly? 18 min](https://sandboxphysics.com/labs/subradiant-atomic-array/)
114. [Quantum & fields Dirac Trembling Motion Why does a free Dirac wave packet tremble when no force acts on it? 18 min](https://sandboxphysics.com/labs/dirac-trembling-motion/)
115. [Quantum & fields Klein Wave-Packet Tunnelling Why can a higher barrier let a Dirac wave packet through when a lower one reflects it? 18 min](https://sandboxphysics.com/labs/klein-wavepacket-tunneling/)
116. [Quantum & fields Kerr Cats & Wigner Interference How can one wave packet of light end up in several places at once? 18 min](https://sandboxphysics.com/labs/kerr-cat-interference/)
117. [Quantum & fields Quantum Backflow on a Ring Can the probability current on a ring flow backward when every momentum points forward? 18 min](https://sandboxphysics.com/labs/quantum-ring-backflow/)
118. [Quantum & fields Quantum Walk & Phase Traps How does a quantum walk differ from an ordinary random walk? 18 min](https://sandboxphysics.com/labs/coined-quantum-walk/)
119. [Quantum & fields Quantum Kicks & Dynamical Localization If you keep kicking a quantum rotor, can its momentum stop spreading? 18 min](https://sandboxphysics.com/labs/quantum-kicked-rotor/)
120. [Quantum & fields Quantum Carpet & Revivals Why does a wave spreading in a box come back to its starting shape? 18 min](https://sandboxphysics.com/labs/quantum-carpet-revivals/)
121. [Quantum & fields Molecular Alignment Revivals Why do molecules line up again long after the laser pulse has passed? 18 min](https://sandboxphysics.com/labs/molecular-alignment-revivals/)
122. [Quantum & fields Matter-Wave Collision What happens when two clouds of condensed atoms overlap? 20 min](https://sandboxphysics.com/labs/condensate-matter-wave-collision/)
123. [Quantum & fields Quantum Vortex Studio How can you tell that a hole in a condensate is a quantized vortex? 20 min](https://sandboxphysics.com/labs/quantized-vortex-dynamics/)
124. [Quantum & fields Bose–Hubbard · Count the Fluctuations What happens to atoms in a lattice as their repulsion grows? 25 min](https://sandboxphysics.com/labs/bose-hubbard-lattice/)
125. [Quantum & fields Fermi–Hubbard · Read the Spin Neighbors Why do neighbors prefer opposite spins? 25 min](https://sandboxphysics.com/labs/fermi-hubbard-spin-correlations/)
126. [Quantum & fields Hofstadter Lattice · Split a Band How much flux does it take to turn one band into several? 25 min](https://sandboxphysics.com/labs/hofstadter-butterfly/)
127. [Quantum & fields Magnetic Edge · Find the Boundary State Which states move along the boundary instead of filling the sample? 25 min](https://sandboxphysics.com/labs/magnetic-edge-spectroscopy/)
128. [Quantum & fields How to Read a Particle Collision How do physicists reconstruct a collision they cannot see from what the detector records? 18 min](https://sandboxphysics.com/labs/particle-collider/)
129. [Quantum & fields How a Knot Becomes a Quantum-Field Observable Why does the expectation value of a Wilson loop depend only on the knot type, not on how the knot is drawn? 18 min](https://sandboxphysics.com/labs/knots-and-quantum-fields/)

Keep exploring

[Motion & dynamics](https://sandboxphysics.com/topics/mechanics/) [Waves & optics](https://sandboxphysics.com/topics/waves-and-optics/) [Fields & matter](https://sandboxphysics.com/topics/fields-and-matter/)