quantumlib · pavoljuhas · May 27, 2026 · May 28, 2026 · May 28, 2026 · May 28, 2026
diff --git a/check_cirq_8054/get-total-memory b/check_cirq_8054/get-total-memory
@@ -0,0 +1,14 @@
+#!/usr/bin/gawk -f
+
+BEGIN { FS = "="; }
+
+/^snapshot=[0-9]+$/ {inrec = 1}
+inrec && /^time=[0-9]+/ {t = $2 * 1e-9}
+inrec && /^mem_heap_B/ {mem_heap_B = $2 + 0}
+inrec && /^mem_heap_extra_B/ {mem_heap_extra_B = $2 + 0}
+
+inrec && /^heap_tree/ {
+    print t, mem_heap_B + mem_heap_extra_B;
+    t = mem_heap_B = mem_heap_extra_B = "";
+    inrec = 0;
+}
diff --git a/check_cirq_8054/oom_qsim_simulation.py b/check_cirq_8054/oom_qsim_simulation.py
@@ -0,0 +1,31 @@
+#!/usr/bin/env python3
+
+"""Script to check for maximum number of qubits where QSimSimulator segfaults."""
+
+import gc
+import sys
+
+import cirq.testing
+
+import qsimcirq
+
+assert __name__ == "__main__"
+if len(sys.argv) != 2:
+    print(f"usage: {__file__} num_qubits")
+    sys.exit(0)
+
+nqubits = int(sys.argv[1])
+
+q = cirq.LineQubit.range(nqubits)
+m1 = cirq.Moment(cirq.H.on_each(q))
+m2 = cirq.Moment(cirq.CX(qi, qj) for qi, qj in zip(q[0::2], q[1::2]))
+m3 = cirq.Moment(cirq.measure(*q))
+c = cirq.Circuit(10 * [m1, m2, m3])
+
+my_sim = qsimcirq.QSimSimulator()
+
+gc.disable()
+gc.collect()
+
+state_vector = my_sim.simulate(program=c).state_vector()
+print(state_vector.shape, state_vector)
diff --git a/check_cirq_8054/qsim_simulation.py b/check_cirq_8054/qsim_simulation.py
@@ -0,0 +1,36 @@
+import gc
+
+import cirq.testing
+import numpy as np
+
+import qsimcirq
+
+nqubits = 20
+# nqubits = 24
+
+q = cirq.LineQubit.range(nqubits)
+m1 = cirq.Moment(cirq.H.on_each(q))
+m2 = cirq.Moment(cirq.CX(qi, qj) for qi, qj in zip(q[0::2], q[1::2]))
+m3 = cirq.Moment(cirq.measure(*q))
+c = cirq.Circuit(10 * [m1, m2, m3])
+
+# make reproducible initial_state
+rs = cirq.value.parse_random_state(8054)
+initial_state = cirq.testing.random_superposition(2**nqubits, random_state=rs).astype(
+    np.complex64
+)
+my_sim = qsimcirq.QSimSimulator()
+
+gc.disable()
+gc.collect()
+
+# burn CPU cycles for a few seconds
+for _ in range(50_000_000):
+    pass
+
+state_vector = my_sim.simulate(program=c, initial_state=initial_state).state_vector()
+print(state_vector.shape, state_vector)
+
+# burn CPU cycles for a few seconds
+for _ in range(50_000_000):
+    pass
diff --git a/check_cirq_8054/results/README.md b/check_cirq_8054/results/README.md
@@ -0,0 +1,42 @@
+# Check of memory in qsim simulation before and after cirq PR 8054
+
+2026-05-27
+
+Smallest number of qubits causing OOM crash, checked with
+`oom_qsim_simulation.py` on a Debian box with 65 GB of memory.
+
+- baseline qsim c5bc02394a and cirq f4c35b02090b - OOM for 34 qubits
+- patched qsim 7d05583a00e0 and cirq #8054 (bca9c5c617de) - OOM for 34 qubits
+
+# 2026-05-27 - RUN LIST ------------------------------------------------------
+
+Memory use during `qsim_simulation.py` was collected using
+```
+valgrind --tool=massif python qsim_simulation.py
+```
+The output massif.out.NNNNNN files were converted to memtotal.NNNNNN.dat
+using `get-total-memory` script.
+
+## baseline qsim and cirq ----------------------------------------------------
+
+### nqubits=20 (repeated to check reproducibility)
+
+- memtotal.733604.dat
+- memtotal.736557.dat
+
+### nqubits=24 (repeated to check reproducibility)
+
+- memtotal.737548.dat
+- memtotal.738662.dat
+
+## patched qsim and cirq -----------------------------------------------------
+
+### nqubits=20 (repeated to check reproducibility)
+
+- memtotal.742794.dat
+- memtotal.743107.dat
+
+### nqubits=24 (repeated to check reproducibility)
+
+- memtotal.743990.dat
+- memtotal.745873.dat
diff --git a/check_cirq_8054/results/memtotal.733604.dat b/check_cirq_8054/results/memtotal.733604.dat
@@ -0,0 +1,57 @@
+# time(s) total(B)
+0 0
+0.318674 1829576
+0.800413 1830656
+1.08539 1833280
+1.49621 3965600
+2.04109 11420768
+2.30147 13350360
+2.71264 17712696
+3.18717 19979776
+3.47974 23178960
+3.94386 23966192
+4.24774 22427040
+4.73715 26087592
+5.09345 21787608
+5.64853 34344200
+6.0532 23333832
+6.67339 23801272
+7.04263 24054344
+7.33646 26933312
+7.77634 26572128
+8.36293 31020344
+8.72959 27231152
+9.24349 30566016
+9.75678 29527336
+10.0368 31484856
+10.4515 32861584
+10.8521 34065888
+11.196 35819400
+11.5052 36376264
+12.1185 38817856
+12.5623 40904920
+12.8479 41389864
+13.4064 45973416
+13.7793 47525304
+14.251 46322464
+14.8548 46146888
+15.342 46148840
+15.9343 48427936
+16.4012 51152048
+16.9931 51333688
+17.316 54121000
+17.6824 54812296
+17.942 55830936
+18.3247 97230944
+20.4203 80317544
+44.9443 63538632
+45.2405 73033952
+45.7872 73034656
+46.152 73035184
+46.7043 73035976
+46.9648 73036416
+47.272 73036768
+47.5777 73037208
+47.8414 73037648
+48.1475 73038000
+48.4202 54819616
diff --git a/check_cirq_8054/results/memtotal.736557.dat b/check_cirq_8054/results/memtotal.736557.dat
@@ -0,0 +1,68 @@
+# time(s) total(B)
+0 0
+0.236307 1829576
+0.647684 1830656
+0.901119 1831376
+1.16279 1832096
+1.62568 4855864
+2.04185 9461272
+2.42849 14207000
+2.81795 18432504
+3.1332 26787080
+3.35759 19030624
+3.67212 19919880
+3.88087 21932792
+4.32047 19697448
+4.59238 23449192
+4.92702 21260224
+5.38009 20740552
+5.6907 34344104
+5.93708 22432224
+6.32605 25918408
+6.56992 23932776
+6.91045 23969744
+7.34829 25118072
+7.78408 26126952
+8.07375 30650456
+8.4586 27037128
+8.84373 27238472
+9.32651 31547392
+9.80775 30132232
+10.225 31882384
+10.7115 33497720
+11.0001 34280976
+11.3337 36002080
+11.5094 36332816
+11.8853 39148072
+12.3438 38551040
+12.7539 40231696
+13.0397 40740888
+13.4487 45972408
+13.7677 45479008
+13.9993 45689144
+14.2996 46235768
+14.6829 46144856
+14.9561 46146808
+15.3351 46853200
+15.6352 48174776
+16.0247 49640680
+16.2574 51150992
+16.5575 50554072
+17.0139 53032160
+17.0688 53563424
+17.1723 54119576
+17.2426 55082016
+17.4184 55005768
+17.5942 55047960
+17.7699 55154488
+17.7983 55829528
+18.01 80314912
+18.0148 80314912
+18.1804 97228312
+23.2847 80314912
+48.5587 63536000
+48.7394 72163936
+48.9182 72164200
+49.0973 72164464
+49.2916 80326656
+49.4717 50396696
diff --git a/check_cirq_8054/results/memtotal.737548.dat b/check_cirq_8054/results/memtotal.737548.dat
@@ -0,0 +1,99 @@
+# time(s) total(B)
+0 0
+0.24384 1829216
+0.563657 1829936
+0.813955 1831016
+1.0374 1833280
+1.30225 1839064
+1.70561 5389248
+1.99261 8696200
+2.35874 13350360
+2.64822 17147600
+2.86035 17388056
+3.14753 26787064
+3.44511 19185968
+3.9095 22048144
+4.13106 19868360
+4.49651 23122080
+4.84353 20408176
+5.04188 25635608
+5.38938 20717440
+5.7061 34344200
+6.00614 22499632
+6.30378 24823696
+6.60223 23307216
+6.80059 23870800
+7.12277 24077696
+7.44424 25003520
+7.60505 26300240
+7.92652 27032448
+8.32849 27879688
+8.56962 32657912
+8.89114 27523216
+9.29605 30264464
+9.6176 28986624
+9.86073 29245704
+10.1969 31991528
+10.5187 32886640
+10.8423 33753192
+11.0642 35095552
+11.4298 36270768
+11.7401 37901992
+12.1969 39385016
+12.6205 40904808
+13.0497 40608224
+13.2163 43593096
+13.6085 45439440
+13.8653 49127576
+14.1522 45892904
+14.5152 46145520
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+15.1357 46147960
+15.3823 46178624
+15.5432 47147704
+15.704 47950408
+15.8649 48425552
+16.0267 49284560
+16.1023 49641512
+16.2521 50137968
+16.3066 50643288
+16.335 51151840
+16.496 50422248
+16.6568 50625192
+16.8176 51594632
+16.933 51679648
+16.9482 52507944
+17.0914 53033376
+17.1463 53564384
+17.2499 54120472
+17.3203 55082912
+17.4811 54936168
+17.6419 54878632
+17.8029 55084632
+17.8763 55830184
+20.4396 457805056
+20.5151 457805056
+23.0232 457806120
+23.1632 726376696
+31.0781 457805056
+58.5807 189367920
+59.6161 323858160
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